Open-air rooms (5)
I believe the answer is:
atria
'open-air rooms' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for atria that I've seen before include "Lobbies" , "Open courts of Roman houses" , "Central courts (in ancient Rome or shopping arcades)" , "Covered courts" , "Public spaces with galleries" .)