Severely criticise roofing material (5)
I believe the answer is:
slate
This clue could be a double definition.
'severely criticise' is the first definition.
'slate' can be an answer for 'criticise' (I've seen this before). I'm not certain of the 'severely' bit.
'roofing material' is the second definition.
(I know that slate is a type of roofing material)
Can you help me to learn more?
(Other definitions for slate that I've seen before include "Roofing material or credit recorder" , "Roofing plate" , "Grey metamorphic rock" , "Roof tile or pub credit" , "Stone used for roofing" .)