Voice thanks for erecting chambers (5)
I believe the answer is:
atria
'chambers' is the definition.
(atrium is a kind of chamber)
'voice thanks for erecting' is the wordplay.
'voice' becomes 'air' (both can mean to express something).
'thanks' becomes 'ta' (UK informal version of 'thank you').
'for erecting' shows that the letters should be reversed in order (in a down clue, letters go up).
'air'+'ta'='airta'
'airta' written backwards gives 'ATRIA'.
(Other definitions for atria that I've seen before include "Central courts (in ancient Rome or shopping arcades)" , "Apartments" , "Upper chambers of the heart" , "Roofed central courts" , "Parts of the heart or of Roman houses" .)