Blocks of flats? (4)
I believe the answer is:
pads
This clue is a double definition.
'blocks' is the first definition.
(pad is a kind of block)
'flats?' is the second definition.
(I've seen this before)
'of' is the link.
(Other definitions for pads that I've seen before include "Fleshes out" , "Cricket leg-guards" , "Quarters" , "flats?" , "Apartments; cushions" .)