To draw a room in the shape of a regular octagon, you can:
1- select the plan (focus)
2- position the first point of the room
3- move the cursor to the second point
4- press the enter key
5- modify the length (4m)
6- press the tab key
7- modify the angle (0° or -22.5°)
8- press the enter key
9- press the tab key
10- modify the angle (135°)
11- press the enter key
12- repeat steps 9 to 11 until your room is closed
13- press the escape key

You can use the AdvancedEditing.sh3p plug-in to move or rotate your room.

regular octagon room.jpg