Ghastly house I'd demolished (7)
I believe the answer is:
hideous
'ghastly' is the definition.
(I've seen this before)
'house i'd demolished' is the wordplay.
'demolished' indicates anagramming the letters.
'house'+'id'='houseid'
'houseid' with letters rearranged gives 'HIDEOUS'.
(Other definitions for hideous that I've seen before include "Extremely unpleasant" , "Frightful" , "Ghastly" , "revolting" , "Unsightly" .)