Cardboard(from the dumpster), alu-foil, glue, tape, black paint, newspaper
We had the thought that if we made it round (or almost round) the reflexions would make the result better. And further more to get the angles of the sides spread more out so that it wouldn't cast as much shadow as "the dumpsterdive".
Result defenetly improved, but still in need of reaching higher temp. to cook the food quicker.