Roofing slabs (5)
I believe the answer is:
tiles
'roofing slabs' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tiles that I've seen before include "Thin flat slabs, for roofing perhaps" , "Glazed rectangles used to cover walls or floors" , "Thin flat slabs of fired clay" , "Small oblong slabs used in roofing" , "Roofing materials" .)