Here is a modern, and well appointed, tree house from Texas. Kent Portman’s treehouse sits in a 100 year old Pecan tree and has air conditioning, heating and a skylight.
The 140 square feet treehouse cost $48,000 to build over 4 months. And Portman uses it for daily meditation, as a guest house, and as a studio to conduct massage therapy.
Despite the solid construction (roof and walls built to code and the use of weather proof doors and windows) I wonder how the branches passing through the wall are sealed. In my experience it is nearly impossible to prevent moisture from running down the branch.
Oftentimes rubber inner tube material can be used to make a flexible gasket. 
However, the living tree passing through the interior space is an inherent host to moisture and flora. The worst case scenario is a potential for musty smelling mildew and mold accumulation. Nothing a bit of extra housekeeping can’t take care of.
I think Portman has created a great little place for an alternate business / studio get-away. And, to build it to code with steel supports means it will last a very long time. I also like the spiral stair case used to get up to the deck.
Visit www.treehousemassage.com for more information on Kent’s massage therapy business and to see pictures from the construction process.
[Via Statesman.com]