1.2 million euros according to the video. Of course it was expensive to build, it was a prototype. It was also 1994, the technology has probably gotten cheaper since then. It show possibilities. If you are interested just go to the architects site - his name is Rolf Disch - choose English and Past Projects and read about it. By the way, rotating or swiveling houses isn't a new idea. I saw one (as a futuristic idea) in an old ads book and seem to remember there being a house that turned on rails built in the earlier part of the 20th century somewhere in Germany.

Just wanted to mention that round these parts (not all that far from Stuttgart) willow constructions are pretty common, if not that tall. I don't know if it's a particularly German thing or found all over the place. It seemed a few years ago that kindergartens, schools and people organizing playgrounds and such were all building willow huts, tunnels, fences, tent-like-things and whatnot. The smaller stuff is really easy, willows (at least some sorts) can take a lot of replanting and bending and still grow. If you've got a garden and kids try a willow play house. And you can still appreciate trees, while also being amazed at how things will grow if given the chance.