Father leads a dog back in the building (6)
I believe the answer is:
pagoda
'the building' is the definition.
(pagoda is a kind of building)
'father leads a dog back' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'leads' means one lot of letters go next to another (some letters go in front of others).
'back' says the letters should be written backwards.
'a'+'dog'='adog'
'adog' reversed gives 'goda'.
'pa'+'goda'='PAGODA'
'in' acts as a link.
(Other definitions for pagoda that I've seen before include "Pyramid-shaped Hindu temple" , "Buddhist tower with several stories" , "Buddhist memorial building" , "Sacred many-tiered temple" , "Asian temple with upward curving roof" .)