Do a turn, roaming circular building (7)
I believe the answer is:
rotunda
'circular building' is the definition.
(I've seen this before)
'do a turn roaming' is the wordplay.
'roaming' indicates anagramming the letters.
'do'+'a'+'turn'='doaturn'
'doaturn' with letters rearranged gives 'ROTUNDA'.
(Other definitions for rotunda that I've seen before include "Round domed building" , "Round domed room" , "Do a turn (anag) -- circular domed building" , "Circular building with a dome" , "circular construction" .)