Rate the new building (7)
I believe the answer is:
Here is my best explanation:
'building' is the definition.
(theatre is a kind of building)
'rate the new' is the subsidiary indication.
'new' is an anagram indicator.
'ratethe' anagrammed gives 'theatre'.
(Other definitions for theatre that I've seen before include "Room for surgery", "Eg, Oxford's Sheldonian", "Scene of operations or dramatic performances", "Drama venue", "Location for plays and operations", "Scene of action", "Building for dramatic art", "Playhouse - operations room", "Space for dramatic art and surgery" and "Building for plays or operations".)