So there has been some discussion...and frustration...with expanding the octagon shaped rooms.
If you dont want to draw the room by hand, here is how you can expand the octagon and still have all sides be the same length.
Just pull the walls in this order 12o'clock...3o'clock...5o'clock and 7o'clock.
Results in an octagon...
but as someone pointed out not all walls are the same length. So...if that is what you want:
End result: a bigger octagon room