I built a client a treehouse last Spring. Actually it wasn't IN a tree, but rather nestled amongst some trees. The posts were from trees I'd reclaimed from treejobs and the 4x16 perimeter boards were from trees I'd gotten milled up. This was more a recycling project for me than anything.
I had 4 days slated for the build, and an 'extra' day for punchlist. I think it ended up taking a total of 17 days and I lost my butt on it. Morale...: Just because you have the ability to do something outside your normal work, doesn't mean you should. -TM-