Roofing slate (4)
I believe the answer is:
tile
'roofing slate' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tile that I've seen before include "Thin slab used to cover roof, wall, floor etc" , "Hat" , "Roofing or flooring item" , "9 for the roof?" , "Mah-jong piece" .)