Type of shed (4-2)
I believe the answer is:
lean-to
'type of shed' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lean-to that I've seen before include "Shed abutting other building" , "Hut" , "Penthouse" , "Shed, outbuilding" , "Building put up against another" .)