E04D3/00—Roof covering by making use of flat or curved slabs or stiff sheets
E04D3/02—Roof covering by making use of flat or curved slabs or stiff sheets of plane slabs, slates, or sheets, or in which the cross-section is unimportant
E04D3/04—Roof covering by making use of flat or curved slabs or stiff sheets of plane slabs, slates, or sheets, or in which the cross-section is unimportant of concrete or ceramics