See this post on Rigel's page for earlier plans. http://happerfamily.weebly.com/rigel/tree-house
We first finished the trap door, then put up some more supporting braces on the other side of the platform, tried to fill in the deck of the platform on the far side, added posts on the corners and in between for the railing. Lastly, we finished covering the deck, leaving spaces for the trees grow through. We're now experimenting with making a netting for the railing, and a rope ladder on one side. Its been a wonderful, learning experience. We've been getting help from many experts: neighbors, friends, cats, dogs and deer!