Awful building to rent (6)
I believe the answer is:
rotten
'awful' is the definition.
(thesaurus)
'building to rent' is the wordplay.
'building' indicates anagramming the letters.
'to'+'rent'='torent'
'torent' is an anagram of 'ROTTEN'.
(Other definitions for rotten that I've seen before include "Decomposed" , "Decayed, putrid" , "Corrupt; very bad" , "Something is ... in the state of Denmark (Hamlet)" , "unpleasant" .)