Many people have asked for round walls.
I tried to make a round wall with short straight walls, but there's a little bug in the software (?).
I made it with 50 cm walls, each wall rotated 165 degrees. As you can see there are two openings in the wall. If you select the wall and make it thicker, the openings become larger. The error is consistent: if I make the same wall using 195 degree rotation, the same openings appear.

I'm using SH3D 2.1 on a Ubuntu system.

Hans