Count building site first (8)
I believe the answer is:
earliest
'first' is the definition.
(similar in meaning)
'count building site' is the wordplay.
'count' becomes 'earl' (I've seen this in another clue).
'building' is an anagram indicator.
'site' is an anagram of 'iest'.
'earl'+'iest'='EARLIEST'
(Other definitions for earliest that I've seen before include "Original or most previous" , "Nearest the start of a time period" , "With the least delay" , "First occurring" , "Nearest the beginning in time" .)