Elevated works building maliciously ruined (7)
I believe the answer is:
'maliciously ruined' is the definition.
(to trash is to destroy)
'elevated works building' is the wordplay.
'elevated' is a reversal indicator (in a down clue, letters go up).
'works' becomes 'art' (I've seen this before).
'building' becomes 'shed' (shed is a kind of building).
'art' in reverse letter order is 'tra'.
(Other definitions for trashed that I've seen before include "Vandalised", "Criticised", "completely taken apart", "Destroyed".)