Rooftop spinners (5)
I believe the answer is:
vanes
'rooftop spinners' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for vanes that I've seen before include "Blades of windmill or propellers" , "Weathercocks" , "Blades of a windmill (5)" , "They show wind direction" , "Blades of a windmill or propeller" .)