Building the frame
After the floor joists and floor were laid, it was time to add the frame. I built each of the four walls on the ground, then lifted them into place. Considering I'd never done frame construction before, this went surprisingly fast.
Next came the siding. As it turned out, this was the trickiest part of the whole treehouse, and the part I did worst. (How bad? If I'd put siding on a real house, there would have been a two inch gap between the top of the wall and the top of the siding at the end of each wall. It really is important to get the first piece right...)
Now that the walls were on, the kids were ready to move in. Waiting two to three months from the time Dad started the treehouse was not something that five-year-olds really understand.