Building engineer scorning TUC needing time to break (12)
I believe the answer is:
constructing
'building' is the definition.
('construct' can be a synonym of 'build')
'engineer scorning tuc needing time to break' is the wordplay.
'engineer' is an anagram indicator.
'needing' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
'to break' indicates putting letters inside.
'scorning'+'tuc'='scorningtuc'
'scorningtuc' with letters rearranged gives 'consructing'.
'consructing' placed around 't' is 'CONSTRUCTING'.
(Another definition for constructing that I've seen is " Building".)