Here's a few photos of a dome I designed for a summer school at Imperial College London. It was built in a few hours by the kids on the course.
The dome was about 2.5m or 8feet high. The geodesic dome was made of plastic plumbing pipe and the inflatable dome inside it was made of plastic damproof membrane
The third picture gives an idea of how many people can fit inside.
The only reason I'm in the picture is to show the scale, honest.