Round building or room (7)
I believe the answer is:
rotunda
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">round building</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(architectural term)</span><br/ ><br/ >'<span class="explanation-format__original">room</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(rotunda is a kind of room)</span><br/ ><br/ ></span>
(Other definitions for rotunda that I've seen before include "Do a turn (anag) -- circular domed building" , "Italian Pantheon, for instance" , "Round building or hall" , "Round domed building" , "Round domed room" .)