How about kaleidoscopes? I used to have my 8th graders make them with cylinders from the publishing company in town. All you need is white posterboard and some clear mylar to make a basic mirror system. They had to measure precisely, bring in objects for the object chamber, and decorate the outside with a theme. I had stations set up and had lots of odds and ends for them to use. They were really impressed that they could create something they had originally thought was so complicated. I have a great book, but of course, I have no idea where it is right now.