Final stage of house extension? (4,7)
I believe the answer is:
home stretch
'final stage' is the definition.
(I've seen this before)
'house extension?' is the wordplay.
'house' becomes 'home' (homing is a kind of housing).
'extension?' becomes 'stretch' (stretch is a kind of extension).
'home'+'stretch'='HOME-STRETCH'
'of' acts as a link.
(Other definitions for home stretch that I've seen before include "Where the end is in sight" , "final stage" , "Final section of racecourse" , "Last part of a race" , "It's almost the end" .)