Tower to be evacuated? Excellent suggestion (5)
I believe the answer is:
trace
'suggestion' is the definition.
(synonyms)
'tower to be evacuated? excellent' is the wordplay.
'to be evacuated?' means to remove the middle letters (internal letters are evacuated from the word).
'excellent' becomes 'ace' (ace can informally mean very good).
'tower' with its centre removed is 'tr'.
'tr'+'ace'='TRACE'
(Other definitions for trace that I've seen before include "Smidgen" , "Track down or make copy" , "Cater (anag.)" , "Small quantity; find" , "Find; copy; small amount" .)