anyone build cabins?

Love the idea, but the width concerns me. 12' is not enough room to have two exterior walls, bathroom, interior wall, room to walk around the bed, and finally the bed. By the time you add the walls all together and the bathroom width you're only left with a 6' wide bedroom. If you want to be able to walk around a bed and access to the shelves as shown in the layout the only option I see might be a twin bed and it will be tight even with that. I wish I had a guest house as it would make life so much easier.

Tom