Central area in a building open to the sky (6)
I believe the answer is:
atrium
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">central area in a building open to the sky</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for atrium that I've seen before include "Entrance hall" , "Central hall of shopping mall etc" , "Central area in a building, open or with a glass roof" , "Central court of ancient Roman house" , "Central hall or court" .)