wow, that really is awesome! what kind of plastic did you use? A friend mentioned a kind of formplastic (don´t know if it´s the right term in english.." from america, but we don´t have something like that in germany .__.
I always use PVC sewering pipes for plastic. They don't sell Sintra PVC sheets over here either, so I tend to use the plastic sewer and plumbing pipes as an alternative. Works like a charm