Figure to open a shop at the flat (5)
I believe the answer is:
seven
'figure' is the definition.
(seven is a number)
'open a shop at the flat' is the wordplay.
'open' suggests taking the first letters (take the opening letter).
'at' means one lot of letters go next to another.
'the flat' becomes 'even' (level).
The first letter of 'shop' is 's'.
's'+'even'='SEVEN'
'to' acts as a link.
(Other definitions for seven that I've seen before include "Number of sisters in Sussex" , "VII" , "Cube root of 343" , "Number of seas sailed?" , "See 1" .)