Roofing slab (4)
I believe the answer is:
tile
'roofing slab' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tile that I've seen before include "Flat piece of ceramic" , "Roofing or flooring item" , "Hat" , "Mah-jong piece" , "Ceramic slab for roofs, walls, floors etc" .)