Round hole through a second floor to the first

[dgavin]

Draw two semicircular walls sarting the 2nd at the end of the first. Adjust the shape shape of the wall(s) as needed to get a proper circle. THen draw another wall from onr of the semi circular walls to an exterior wall.
(Chief does not like "island" rooms). Make all three walls invisible. Designate the round room as open below. Done. IF you want a railing or half wall select the semi-circular walls and make them railings and don;t make them invisible.