Is let off roofing (5)
I believe the answer is:
tiles
'roofing' is the definition.
(I've seen this in another clue)
'is let off' is the wordplay.
'off' is an anagram indicator.
'is'+'let'='islet'
'islet' anagrammed gives 'TILES'.
(Other definitions for tiles that I've seen before include "Thin flat slabs of fired clay" , "Thin flat slabs, for roofing perhaps" , "Roofing materials" , "Glazed rectangles used to cover walls or floors" , "Small oblong slabs used in roofing" .)