Shed with a sloping roof, adjoining another building (4-2)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
lean-to
(Other definitions for lean-to that I've seen before include "Building supported by another" , "Small building attached to larger one" , "It's roof slants against a wall" , "Building with roof resting against larger building (4, 2)" , "Structure whose roof has only one slope" .)