Paul-those chairs look great and that site seems really cheap! £2.50 for 6 chairs! He's got a few good things on that site. I especially like the library set with the globe and bookshelves. I might try and build benches in the style of those chairs.
Neil-The plastic sheet is only the thickness of a sheet of paper. Easily bendable. The model gets the strength from the frame on the inside. As well as the circular framework there's also straight sections running the length of the corridor.
Hammers- as Jim says, just take your time with the cutter. Don't try and cut the circle out in one go. There's two cutters myself and Colin use to build things. Ones that compass thing and the other is a hole punch. I'll try and take a picture of it. I think we got it out of Millars the art store.