WO 2009/108985 PCT/AU2008/000322 1 A roof structure for a transportable building FIELD OF THE INVENTION The present invention relates to a roof structure for a transportable building and, in particular, to a roof structure for use in transportable buildings in a portable camp. The roof structure is pre-wired in that 5 it includes electrical, gas and other utility cables mounted inside the roof. The cables are arranged so that they each suspend from the ceiling at predetermined locations according to a particular building layout, enabling fast and efficient construction of the buildings. BACKGROUND OF THE INVENTION Camps have been used for many years to provide shelter and accommodation especially in 10 remote areas. This is especially so in the case of remote camps that are assembled using a number of transportable buildings, some of the buildings used as sleeping quarters, others as the kitchen and dining room facility and others still as recreational areas. It is not uncommon for a camp to consist of sixty to eighty buildings that can accommodate several hundred people. These camps are completely self-contained in that the transportable buildings provide all of the 15 facilities for a small remote community that may be needed in a particular area. Accordingly these camps include all of the modem day facilities such as electrical power, water, sewerage, and communication. They therefore typically also include their own power generation systems, water distribution systems, sewerage treatment plants, and communication facilities such as satellite dishes. The camps typically require a considerable amount of skill, time, and effort to assemble and commission. Once constructed, 20 these camps can however provide accommodation indefinitely if the infrastructure is maintained. In some instances the camps have to be portable or mobile. For example, during construction of infrastructure across a vast area, such as roads or pipelines supplying water or gas, a particular location for a camp housing the construction workers, may only be viable for several weeks or months. As the pipeline is progressively constructed, there is a balance between the economic cost of the travel time of 25 workers housed in the camp to the current work site and time spent constructing the actual pipeline. It is therefore accepted in the industry that if the travel time between a camp and the work location is more than an hour, a new camp has to be constructed that is closer to the work location. At that time, a new camp is therefore constructed one hour ahead of the current construction location or generally up to several hundred kilometres away from the existing camp. 30 Each building in the camp will typically include the same predetermined layout. For example, inside each transportable building there are a plurality of appliances which require the supply of electricity and/or gas to operate, including indoor and outdoor lights, wall mounted power outlets for WO 2009/108985 PCT/AU2008/000322 2 appliances such as bed lamps, air-conditioning units, etc, and all of the locations of each of these appliances are standard across all buildings. Typically, cables used to connect electricity to such appliances are made to extend from an external area, for example from a power generator or from another building inside the camp, to inside the building through apertures in the walls and/or ceiling. The cables 5 are then carried within cable holders or housings which line the walls and ceiling and extend to the respective appliances. For example, where the cables are fed in through the wall, there may be a cable holder lining the ceiling to reach the lights (typically located at the centre of the building), along the walls so that cables can be fed to appliances on the opposite side of the room, and possibly to further buildings in series, and vertically down the walls to power outlets and the like. 10 There are a number of problems with this conventional method of "wiring up" modular buildings. Quite a significant amount of cables are required to supply any one building in a camp with electricity and gas. For this reason, wiring up such buildings can be a cumbersome and often time confusing task. In addition, because all of the cables extend inside the building from one point, a significant amount of cable housing is required, which is not only costly but also unsightly. Furthermore, 15 because of the complexity of the wiring process, skilled personnel such as electricians are required on-site during construction of the buildings to ensure that the buildings are wired safely and according to regulation. Because commissioning and decommissioning of portable camps is required to be undertaken as fast and efficiently as possible, any means of minimising time and cost restraints is advantageous. For 20 example, the less skilled workers that are necessary to assemble the buildings, the less expensive the process is, because unskilled workers who are already occupying the camps can be employed to do certain jobs. In using the conventional system described above, not only are more parts required in the form of cable housings and the like, significantly more time is required to wire up each building. There is therefore a need for a more fast, efficient, less complex, and more cost-effective means of wiring up 25 transportable buildings in a portable camp. In addition, there is a need to be able to wire up such buildings in a more aesthetically pleasing manner. It is an object of the present invention to overcome at least some of the abovementioned problems or provide the public with a useful alternative. It is a further object of the present invention to provide a roof structure for use on a modular 30 building including a ceiling having pre-drilled apertures for accommodating a network of electrical cables, gas conduits and the like, whereby the apertures are positioned according to a predetermined building layout. SUMMARY OF THE INVENTION WO 2009/108985 PCT/AU2008/000322 3 Therefore in one form of the invention there is proposed a roof structure for a transportable building, said roof structure characterised by: a frame adapted to be fixed above side walls of said building, said frame further adapted to house utility supply means for said building; 5 a ceiling associated with said frame, said ceiling including a plurality of apertures located at predetermined positions on the ceiling according to the location of utility supply destinations inside said transportable building, each aperture adapted to receive the utility supply means corresponding with the utility supply means destination. In preference each aperture is positioned as close as possible to each corresponding utility supply 10 destination. Preferably when said utility supply means is in the form of an electrical cable, said utility supply destination being a corresponding electrical appliance inside said transportable building. In preference said electrical appliance is in the form of a light, a light switch, or a power outlet. Preferably when said utility supply means is in the fornm of a gas conduit, said utility supply 15 destination is a'corresponding gas appliance inside said transportable building. Preferably said gas appliance is in the form of an air conditioner, a gas fired oven, or a freezer. Preferably said frame includes two longitudinal girders spaced apart and connected by a plurality of cross members or purlins to form a substantially rectangular structure. In preference said ceiling comprises a plurality of ceiling panels extending transversely between 20 said longitudinal girders. Preferably each adjacent ceiling panel is connected using joining strips. Preferably said ceiling is fixed between said girders using a chemical bonding foam. Advantageously said chemical bonding foam also acts as roof insulation. In preference said purl ins are fixed at their highest position at the centre of the girders, and at 25 their lowest positions at the ends of the girders, to thereby ensure that roofing panels fixed above said purlins are slightly concave to facilitate water run-off. Preferably utility supply housings extend from said apertures to said destinations along the internal walls and ceiling of said transportable building, said housings adapted to house and conceal the utility supply means. CI IRtTITI ITI- CII-T IDI II I- 2 D Pn/Ai I WO 2009/108985 PCT/AU2008/000322 4 BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several implementations of the invention and, together with the description, serve to explain the advantages and principles of the invention. 5 In the drawings; Figure 1 illustrates a modular building having a pre-wired roof structure in accordance with the present invention: Figures 2a-2c illustrate from a front, top and side view an elevated platform which may be used in the construction of the roof structure of Figure 1; 10 Figure 3 illustrates a perspective view of the elevated platform of Figure 2; Figure 4 illustrates a top view, following the first stage of construction, of the frame and ceiling panels of the roof structure of Figure 1; Figure 5 illustrates a perspective view of Figure 4; Figure 6 i llustrates a top view, following the second stage of construction, of the frame and ceiling 15 panels of the roof structure, the ceiling panels including apertures for accommodated electricity cables and the like; Figure 7 illustrates a perspective view of Figure 6, Figure 8 illustrates a top view, during the third stage of construction, of the frame and ceiling panels of the roof structure having foam insulation material sprayed between each frame 20 member and the adjacent ceiling panels; Figure 9 illustrates a perspective view, following the fourth stage of construction, of the frame and ceiling panels of the roof structure after foam has been sprayed above the entire ceiling area; Figure 10 illustrates a top view, during the final stage of construction, of the frame, ceiling panels 25 and foam insulation of the roof structure being the lengthwise laying of corrugated roofing panels above the frames; and Figure 1 illustrates a perspective view of the fully constructed roof structure of the present invention. CI IIRTITI IT- CI-FIFT IPI l F 9AI P(VAI I WO 2009/108985 PCT/AU2008/000322 5 DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description of the invention refers to the accompanying drawings. Although the description includes exemplary embodiments, other embodiments are possible, and changes may be made to the embodiments described without departing from the spirit and scope of the invention. 5 Wherever possible, the same reference numbers will be used throughout the drawings and the following description to refer to the same and like parts. Referring to Figure 1, there is illustrated a roof structure 10 of the present invention fixed above a transportable building 12. The building includes a floor 14, parallel ends 16 and 18, and longitudinal side walls 20 and 22, and doors 24 located on side wall 20. Of course, the geometry of the building may vary 10 and it is not intended to limit the present invention to the same exact type of building. The building 12 is mounted on a chassis 26 that may include channels 28 allowing each building to be handled by a forklift (not shown). The building 12 is mounted above stacked and spaced apart footing members 30, however, leg supports (not shown) could equally well be provided at the corners of the chassis to position the buildings on a site. Furthermore, the leg supports could include self-levelling 15 means. The roof structure 10 of the present invention is shown in its completed form in Figures 1 and I1, and at its various stages of construction in Figures 4-10. The roof 10 comprises two longitudinal, C-section girders 32 and 34 which are inwardly directed, and a plurality of equally spaced purlins 36 extending between the girders 32 and 34. The purlins 36 are 20 positioned in a curved manner along the length of the girders whereby the purlins are at their highest position in the middle of the girders, and at their lowest positions towards the ends of the girders 32 and 34. The skilled addressee would realise that because roof sheeting 38 is adapted to be fixed directly above the purlins 36, as will be described further below, they need to be positioned like so to facilitate water run-off from the roof sheeting. There are also two vertically aligned end purlins 40 and 42, and 44 and 46 25 positioned one above the other at the ends of the girders, which cap the roof structure 10. Forming part of the roof structure is a ceiling 48, the bottom surface of which is flush with the bottom surface of the C-section girders 32 and 34 which line opposed sides of the ceiling. Effectively, the ceiling 48 extends between the C-section girders 32 and 34. As described in more detail below, polyurethane foam 50-is sprayed between the ceiling 48 and frame members, not only for insulation 30 purposes, but also as a means of binding the ceiling and the surrounding frame member, including with the girders 32 and 34, without the need for mechanical fasteners such as screws, bolts and the like. CI IRCTITI IT- CI-FIFT IPI l - 9AI P(VAI I WO 2009/108985 PCT/AU2008/000322 6 As mentioned in the preamble of the invention, transportable buildings constructed on a large scale, for example for use in a portable camp, are typically identical and constructed according to a predetermined layout. This obviously reduces time and cost during construction, and during commissioning and decommissioning of camps. For example, the position of the lights, the position of the 5 air conditioner, and the position of the power outlets on the walls are typically all predetermined. The ceiling 48 of the roof structure 10 of the present invention is also constructed in accordance with this predetermined layout in that during its construction, apertures 52 are drilled where each electrical or gas appliance is located so as to accommodate cables and conduits 53 for supplying such appliances. For example, there may be an aperture 52 located at the centre of the ceiling 48 for 10 accommodating wiring corresponding with the main light. Similarly, there may be apertures 52 in the ceiling 48 adjacent the walls for accommodating wiring which corresponds with power outlets on the side wall or light switches. Where there is an air conditioner (not shown) mounted on a wall of the building, apertures 52 would be present in the ceiling 48 at the precise position there above to accommodate the electrical wiring and gas conduits. 15 In the embodiment shown in Figures 2-3, a construction platform 54 is used in the manufacture of such a roof structure. The platform 54 is made up of a horizontal frame 56 comprising various structural members 58 supported above legs 60, the legs 60 having rollers 62 at lower ends thereof for facilitating movement of the platform 54. Supported above the frame 56 is a horizontal support surface 64, preferably made of wood, above which the roof structure 10 of the present invention is to be constructed. It is to be 20 understood that although the platform 54 is the preferred apparatus used to manufacture the roof structure 10, the present invention is not intended to be limited to only this means of manufacture. The horizontal surface 64 is preferably marked up according to the size, shape and utility layout of the building. For example, the width and length of the roof structure 10 could be marked on the top surface using an appropriate marking means. There is also a plurality of pre-drilled guide holes 66 25 extending through surface 64 according to the pre-determined building layout. In particular, the guide holes 66 are positioned in correspondence with the position of various electrical/gas items inside the building such as lights, power outlets, switches and air conditioning systems. Therefore, the various steps'of construction are outlined as follows: 1) As mentioned, the surface 64 is preferably marked up so that the width of the building is known 30 and the assembler can simply place the girders 32 and 34 in their correct spaced apart locations on the surface. In preference, the longitudinal girder 34 is placed right up against one longitudinal side of the platform 54 while the other girder 32 will typically be placed inwards of the other longitudinal side, the surface 64 being wider on that side so as to also provide walking space alongside the roof structure during construction. L-shaped brackets 68 can be used to abut against CI IIRTITI IT- CI-FIFT IPI ll - 9AI P(VAI I WO 2009/108985 PCT/AU2008/000322 7 the outer side of girder 32 so as to maintain it in position throughout the construction process. As also mentioned, two vertically disposed end purlins are mounted between the girders 32 and 34 at ends thereof. The two end purlins are preferably mounted to the girders using mechanical 5 fastening means such as a nut and bolt connections. 2) The next step in the process is the laying down of the ceiling 48. The ceiling 48 is preferably made of strong, slightly flexible, waterproof material. Such material is typically shipped in panels 70 and so rather than having a single ceiling structure, the ceiling will typically be made up of a plurality of connecting panels 70. The plurality of panels 70 making up the ceiling 48 can be seen 10 clearly in Figure 4. It is to be understood that a large single panel could equally well be used, although this is not practical as the surface area of the ceiling is quite large. As mentioned earlier, the ceiling panels 70 are not bolted to the girders or end purlins, they are simply placed above surface 64 so that they are located inside the respective frame members. 15 Separating each panel are plastic joining strips (not shown) which serve to connect adjacent panels and thereby fill the gap there between and offer a more pleasing appearance from inside the room. Such strips are well known in the art. Therefore at the end of this step, the basic rectangular frame of the roof structure 10 is 20 established, and the ceiling panels 70 are laid in place and coupled via joining strips, 3) Once the ceiling panels 70 are in place, the apertures 52 which accommodate the various cables 53 need to be drilled into the ceiling 48. This is achieved by drilling upwards through the pre drilled guide holes 66 present in the platform surface 64 mentioned earlier. Those skilled in the art would realise that in doing so, the same guide holes 66 that are present in the platform surface 25 64, will be formed in the ceiling 48. This is the reason the platform 54 is elevated, so that there is access to beneath the structure for drilling the ceiling apertures 52. Mounted on one side of the platform 54, there is a black board 72 supported by posts 73. The purpose of the black board 72 is to mark out which electrical appliance, for example, corresponds 30 with a particular aperture 52 in the ceiling 48. For example, a light switch (not shown) located on the near side of the building 12 could be marked out on the bottom of the blackboard 72 in the relevant longitudinal position, whilst a power outlet (not shown) located at the same longitudinal position but on the opposite wall of the building 12 could be marked out on the top of the blackboard 72, and so on. It is then easier for an electrician or other worker to wife up the roof 35 structure 10, and further roof structures there after, using the same platform 54. QI IIRZTITI ITI- CIIT IPI II I- P2n/AI I WO 2009/108985 PCT/AU2008/000322 8 4) The next step is wiring up the roof structure 10 which involves inserting the plurality of electrical cables and gas conduits 53 through one end of the roof (preferably below the lower of the two end purlins 40 and 42, or 44 and 46, through to the respective apertures 52 in the ceiling 48. All wiring and cables that are required to supply the building are run through the roof structure 10 5 and down into the corresponding ceiling apertures 52. As shown in Figure 7, approximately 2 metres of cabling is fed through each aperture 52 to allow for it to extend to a corresponding appliance. Obviously, any length of cable could be fed through depending on the distance of the appliance from the ceiling 48, for example, the central light may 10 only a require a small length of cable, whilst a power outlet located at the bottom of the building may require 2-3 metres. 5) Once the ceiling 48 is laid, the purlins 36 which extend between the girders 32 and 34 may be connected. This step could have been undertaken prior to steps (2), (3) or (4) above, however, in preference this step is done afterwards so that the purlins do not form an obstruction to the 15 person(s) laying the ceiling and wiring up the roof. The purlins 36 are simply bolted at their opposed ends to the girders 32 and 34 using known mechanical fastening means, and as mentioned earlier, are raised toward the centre of the girders and lowered towards the ends to facilitate rain water run-off. 20 Therefore at the end of this step, the complete frame of the roof structure 10 is established, as is the ceiling 48, Furthermore, the roof structure 10 is completely wired. 6) In order to now bind the ceiling 48 with the surrounding roof frame members 32, 34, 36, 42 and 44, and to secure the network of cables and conduits 53 in place, polyurethane foam 50 is sprayed above the ceiling 48. The foam 50 has been developed such that when it is exposed to air it 25 hardens to form a rigid insulation material for the roof 10. The foam also has exceptional chemical bonding properties so that foam 40 which contacts both the ceiling 48 and various frame members, bonds the two structures together, hence why no mechanical fastening means are required to secure the ceiling in place. 30 In preference, the foam is firstly sprayed between the ceiling 48 and each of the purlins/girders in order to ensure that the ceiling 48 is securely fixed, as shown in Figure 8. Then once this is completed, the remainder of the ceiling 48 can be sprayed until an adequate amount is present for the purpose of insulating the building 12 as well as securing the network of wiring and conduits 53 above the ceiling 48 in their designated positions. Obviously the foam 50 should not exceed WO 2009/108985 PCT/AU2008/000322 9 the height of the purlins so as to allow for the roofing panels 38 to be fixed, as described in step (7) below. 7) The final step in constructing the roof structure 10 of the present invention is the laying down and bolting of the longitudinal roofing panels 38. In the embodiment shown, the roofing panels 38 are 5 corrugated roofing panels which extend the entire length of the building structure, however, other configurations are possible. The panels 38 are preferably laid starting at one side of the structure 10 and finishing on the other, with each panel being bolted down at spaced apart positions along the transverse purlins 10 36. As mentioned, the purlins are at their highest position in the middle portion of the girders 52 and 54, and extend in between the two end purlins 40 and 42 on one side, and 44 and 46 on the other. The panels 38 are preferably fixed above the lower of the two end purlin pairs 42 and 44. It is to be understood that the present invention is not intended to be limited to the location of the guide holes 66, or the number/arrangement of cables and conduits 53, to that which is illustrated in the 15 drawings. These are shown by way of example only. For example, there may be four separate sleeping quarters in any one transportable building 12. In such circumstances, the network of cables/conduits 53 and the location of the apertures 52 in the ceiling 48 would be a lot more complex compared to that which is shown in Figure 6 for example. It is to be further understood that the roof structure could equally house other supply items such as water and sewage pipes and is not intended to be limited to only electricity and 20 gas supply only. Furthermore, it is envisaged that all parts used in the roof structure 10 will be manufactured specifically to ensure even more fast and efficient construction. For example, rather than drilling the apertures 52 by the means described above, each individual ceiling panel 70 could be pre-manufactured so that they include pre-drilled apertures 52. Further still, each panel 70 could be numbered according to 25 their position on the roof for ease of installation. The skilled addressee would realise the benefits in simply having to lay down the pre-drilled panels in numbered order between the frame members. Similarly, the girders 32 and 34, and purlins 36, could include pre-drilled apertures for accommodating bolts, for example, at the various positions where the structural members are intended to be connected. The advantages of the roof structure 10 of the present invention should now be evident. Once 30 constructed, the roof structure 10 can simply be mounted above the walls of a transportable building 12, and fixed thereto using known construction methods. All of the electrical wiring, gas conduits, and the like, are fed into the roof structure 10 and secured therein. The cables, etc, are arranged inside the roof 10 so that each cable extends to an aperture corresponding with the position of the intended appliance. Those skilled in the art would appreciate the time and cost savings in using such a roof structure 10, particularly WO 2009/108985 PCT/AU2008/000322 10 during commissioning and decommissioning of portable camps, when compared to conventional roof structures for transportable buildings. Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to 5 be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus. In any claims that follow and in the summary of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of 10 "including", i.e. the features specified may be associated with further features in various embodiments of the invention.