Show preference for a penthouse (4-2)
I believe the answer is:
lean-to
'a penthouse' is the definition.
(I've seen this before)
'show preference for' is the wordplay.
'show preference' becomes 'lean' (I've seen this in another clue).
'for' becomes 'to' (eg both can mean 'in the opinion of').
'lean'+'to'='LEAN-TO'
(Other definitions for lean-to that I've seen before include "Outhouse" , "Building put up against another" , "Small building resting on side of larger one" , "greenhouse, perhaps" , "Building propped against the wall of another" .)