Discard outbuilding (4)
I believe the answer is:
shed
I believe 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)
(Other definitions for shed that I've seen before include "Outhouse for storing garden tools etc" , "storage building" , "Get rid of - hut" , "Outhouse -- cast" , "Shack" .)