Building's unprofitable, as well as lacking love (4-2)
I believe the answer is:
lean-to
'building's' is the definition.
(type of structure built against another building)
'unprofitable as well as lacking love' is the wordplay.
'unprofitable' becomes 'lean' (similar in meaning).
'as well as' becomes 'too'.
'lacking' is a deletion indicator.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'too' with 'o' taken out is 'to'.
'lean'+'to'='LEAN-TO'
(Other definitions for lean-to that I've seen before include "Penthouse" , "It's roof slants against a wall" , "Shed built against wall" , "Building with roof resting against larger building (4, 2)" , "Small building resting on side of larger one" .)