Don't get me wrong, some of those crazy-expensive Pete Nelson-style treehouses are total and absolute art, and I love them myself, but they lack one big thing- accessibility. I mean how many of us will ever be able to afford one of those- never mind the land they'd need to reside on. Very few of us.
So... for all us comparatively "poor" folks who need to keep it real, here's a TINY treehouse sleeper I designed that...
-Costs VERY little
-Is EASY to construct
-Is light enough in panelized form where you could walk each piece into the woods by yourself
-Is so incredibly small that it would be easy to hide- OR code/your town won't even care about it.
It could also be used as a tiny greenhouse, a cold frame (coldframe) for early season gardening, or as a modern chicken coop. And I'm sure there are other options or uses for it as well.
The one shown is more of a "stilt house" than a tree fort or treehouse, but you get the ideas and the new plans lay it all out for you.
It's all stock materials too, including the Suntuf Polycarbonate roofing that you'll use for the clear front wall.
You can find more on Suntuf here- https://www.palram.com/us/?redirect_info=US%2Cen%2CUnited%20States