Houses on posts
DIY Network project
Well illustrated playhouse build with some good tips.
Ron Hazelton's Housecalls
Building a platform that sits within a tree, although support comes from posts and a brick wall.
Miso Barrel treehouses in Japan
These houses were built at much cost and legal battle and are at the height of luxuriance. They were built from huge recycled soy sauce barrels.
Tom Norian's treehouse
A cleverly designed staircase both supports the house and keeps children using it safe from falls. Built in a California Craftsman style.
Treehouse time lapse
Clear time lapse video of a small treehouse being constructed between two trees.