Allow students to use any materials they wish, but insist that the models be accurate. I have done this with upper and lower level classes and the results are interesting and sometimes quite impressive. I have had models made of cereals, candies, Christmas lights, golf tees, nuts and bolts, styrofoam balls, pine cones, and balloons, among other things. Create a brochure for a genetic disease. Sample brochures for such common diseases as cancer and heart disease can be displayed as models.
Students love to do puzzles and play games.
With a little imagination, various kinds of puzzles can be created. The students themselves may enjoy making hidden word or crossword puzzles for others. Other types of puzzles could be games based on popular television programs such as Jeopardy, Family Feud, and Wheel of Fortune. Book companies are generous in sending examination copies of their books. Textbooks will give you much background information and can also be used as student resources if you're willing to let them get their hands on your books.