simply put there would be no mediocre budget for what your wanting to do, a bathroom, full kitchen and bedroom ?....The plumbing and electrical alone will dictate city approval and how your going to get the toilet plumbed to the house plumbing (which you will have to do) is not going to be cheap.
YES there should be extra room left in the bedroom of your tree house in case you get married, where else would you expect your new wife to sleep>>>> in a real house with a roof ?
