Elevator for part of the building (4)
I believe the answer is:
wing
This clue is a double definition.
'elevator' is the first definition.
(wings are used to elevate or fly)
'part of the building' is the second definition.
('wing' is part of 'building')
'for' acts as a link.
(Other definitions for wing that I've seen before include "attacker on side" , "Branch (of a hospital building etc)" , "Take . . . . to fly like a bird" , "Projecting part of bird or aircraft" , "Footballer" .)