Here ya go,
Make a solar powered marshmallow roaster
What we will need:
1. A page magnifier. More technically known as a Fresnel lens (pronounced freh-nell), this is a piece of plastic almost the size of a notebook page (7 inces by 10 inches) that is used to magnify a page of a book to make it easier to read. These are available in drug and stationery stores, and also in our catalog.
2. A small cardboard box. The actual size will depend on the focal length of the magnifier. The magnifier we use focuses the sun to a small bright dot at a point 10 and a half inches from the lens. This means that a box 10 inches on a side would be perfect. The actual dimensions are not critical, as we will discuss ways to adjust for large or small boxes.
3. A package of bamboo skewers to hold the marshmallows. You can also use coat-hanger wire, or long fondue forks.
4. Some aluminum foil.
5. Some glue.
6. Some tape.