Building's effect initially provided in cubes (7)
I believe the answer is:
edifice
'building's' is the definition.
(synonyms)
'effect initially provided in cubes' is the wordplay.
'initially' suggests taking the first letters.
'provided' becomes 'if' (eg 'provided it's sunny' means 'if it's sunny').
'in' is an insertion indicator.
'cubes' becomes 'dice' (I've seen this in another clue).
The first letter of 'effect' is 'e'.
'if' inserted within 'dice' is 'difice'.
'e'+'difice'='EDIFICE'
(Other definitions for edifice that I've seen before include "'Large, imposing building (7)'" , "Monument" , "impressive pile!" , "Grand building" , "Impressive building" .)