Number a chapter at the start, building story (7)
I believe the answer is:
account
'story' is the definition.
(synonyms)
'number a chapter at the start' is the wordplay.
'number' becomes 'count' (count is a kind of number).
'chapter' becomes 'c' (abbreviation).
'at the start' means one lot of letters go next to another.
'a'+'c'='ac'
'count' after 'ac' is 'ACCOUNT'.
'building' acts as a link.
(Other definitions for account that I've seen before include "Bill; description" , "books" , "Narrative or invoice" , "Bill; importance" , "Invoice - story" .)