Baby's bed, which is let down from top of building (6)
I believe the answer is:
cradle
This clue is a double definition.
'baby's bed' is the first definition.
(cradle is a kind of baby's bed)
'which is let down from top of building' is the second definition.
(cradle can mean a structure holding a worker)
(Other definitions for cradle that I've seen before include "Rocking cot" , "'When the bough breaks, the . . . . . . will fall'" , "Baby's cot" , "Hold lovingly" , "One for rocking baby" .)