An old door some chalkboard paint.
Roundup: New Takes on Old Doors
Birds on a wire curtain....The Graphics Fairy - DIY: Gorgeous Decor at the April 2013 Design House at Lucketts Store
Rustoleum's NeverWet - invisible until it rains
Tree House Plans - How to Build a Backyard Tree House - Popular Mechanics
Bainbridge Island, WA Spring 2003 Built for Sunset's book "Kids Places to Play," this is an example of how a treehouse can be built with all off the shelf materials (except for the salvaged windows, cedar pickets and 2 fabricated nave brackets). The route to the crows nest is thru a trap door. There is ample room for 2 kids in sleeping bags.