Discard an outbuilding (4)
I believe the answer is:
shed
This clue is a double definition.
'discard' is the first definition.
(I've seen this before)
'outbuilding' is the second definition.
(outbuilding in a garden)
'an' acts as a link.
(Other definitions for shed that I've seen before include "Garden store" , "One-storeyed outbuilding" , "Lose as trees do leaves" , "Barn" , "building away from home" .)