Roofing material defective at the front, leaving opening (5)
I believe the answer is:
hatch
'opening' is the definition.
(I've seen this before)
'roofing material defective at the front' is the wordplay.
'roofing material' becomes 'thatch' (thatch is a kind of roofing material).
'defective at the front' means to remove the first letter (the letter at the front is missing).
'thatch' with its initial letter taken off is 'HATCH'.
'leaving' is the link.
(Other definitions for hatch that I've seen before include "Draw fine lines" , "contrive to > emerge in > shade" , "Think up" , "Enter the world" , "Brood" .)