Building of French erected providing formality (7)
I believe the answer is:
edifice
'building' is the definition.
('edifice' can be a synonym of 'building')
'of french erected providing formality' is the wordplay.
'of french' becomes 'de'.
'erected' says the letters should be written in reverse.
'providing' becomes 'if' (I've seen this in other clues).
'formality' becomes 'ice' (I've seen this before).
'de' reversed gives 'ed'.
'ed'+'if'+'ice'='EDIFICE'
(Other definitions for edifice that I've seen before include "Monument" , "Fine building" , "Permanent building" , "Impressive building" , "Construction" .)