Don't make it more difficult than necessary, use a cylinder instead of creating a room:

Drag a cylinder in your 2Dview,
resize as needed (width and depth, height doesn't matter),
set horizontal rotation to X 90°.
Export and import as window.

Much easier than creating a circular room with walls.
The same cylinder can be used as a non-window filler disk when you set its height to the wall thickness and export/import.

One thing: cutting a hole doesn't work on a curved wall. The cutout will always be sqaure.[hr]by-the-way: start a new topic for a new subject.
The cutout problem is not related to the topic title hinge and rail. A new relavant topic title makes it easier when someone searches the forum for a specific problem.