I thought this was awesome. Great work.
I really don't know anything about patents but I'm guessing getting a patent for your design wouldn't really help since people could just change things a bit and not violate your patent. Which is unfortunate because now I've already thought about
stealing using your very cool idea and mass-marketing/selling this concept.
I already looked up plastic or composite materials, such as used for patio storage or sheds and large dog houses, so that you could have a lightweight but durable shell that is easily mobile, and putting in all your improvements (windows, venting, etc.). I wonder if people would buy such a thing? I would also put in a firm foam padding on the floor (couldn't tell if yours had one). Since I'm planning to RE in a few months, I might have to build one and find out if it will sell. At some point though, I'm not certain that this doesn't just blur into things already available like outdoor play houses, tree houses, and yes, sheds.
If you can get that patent, do it before it's too late!