Do a turn, wandering round building (7)
I believe the answer is:
rotunda
'round building' is the definition.
(architectural term)
'do a turn wandering' is the wordplay.
'wandering' is an anagram indicator.
'do'+'a'+'turn'='doaturn'
'doaturn' is an anagram of 'ROTUNDA'.
(Other definitions for rotunda that I've seen before include "Round domed room" , "Do a turn (anag) -- circular domed building" , "Circular room or building" , "Round domed building" , "circular construction" .)