Leaves building site around ten (5)
I believe the answer is:
exits
'leaves' is the definition.
('exit' can be a synonym of 'leave')
'building site around ten' is the wordplay.
'building' is an anagram indicator.
'around' means one lot of letters goes inside another.
'ten' becomes 'x' (roman numeral).
'site' is an anagram of 'eits'.
'eits' placed around 'x' is 'EXITS'.
(Other definitions for exits that I've seen before include "Departs" , "Ways out" , "Withdraws" , "Goes out, leaves" , "Egresses" .)