The essence of the sukkah, for the rabbis, lies in the special thatched roofing, the skhakh, and the shade it gives.
According to halakha (Jewish law), this skhakh must provide more shade than sun but must not block out the stars. It must come from plants that grew out of the ground but that are no longer attached to the ground.
A kosher roof can be bamboo or reed mats or wooden slats covered by palm fronds or other branches.
The photo shows some klutz-proof, easy to carry and put up, sukkah roof kits on sale just outside Jerusalem's Shuk Machaneh Yehuda. Oh, and some colored tinsel to decorate your sukkah, too.
And as luck and good timing would have it, New York's Madison Square Park has just had a dozen of its trees decorated with TREE HUTS, pinewood tree houses perched 30 feet up in the branches! The installation is being built under the direction of Japanese conceptual artist Tadashi Kawamata.
More information and real photos at the fine Daily Dose of Architecture blog. Or enjoy the Tree Huts blog.
Even if they got the skhakh right, I'm afraid these tree huts could not be counted as kosher sukkot. Why? Because nothing, not even a tree (or an overhanging balcony), may come between the sukkah and the sky. If a sukkah is built on the very TOP of a tree, then it is valid. Maybe not so safe, but kosher. . . .
Artist's sketch, from the Tree Hut blog