I left broken toenail in the shed (4-2)
I believe the answer is:
lean-to
'the shed' is the definition.
(I've seen this before)
'i left broken toenail in' is the wordplay.
'i' becomes 'a'.
'left broken toenail' becomes 'lento' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' indicates putting letters inside.
'a' inserted within 'lento' is 'LEAN-TO'.
(Other definitions for lean-to that I've seen before include "greenhouse, perhaps" , "Hut" , "Shed built onto house" , "Small building attached to larger one" , "Shed, outbuilding" .)