I posted a fuzzy picture from a seminar at RTR about a home made solar cooker. One of the presenters later posted a link to a large number of different DIY solar cooker plans.
If you go to Main Page it gives a lot of information on the state of solar cooking as it is now. The previous link is an archive link. I had the question of ‘but does it work?’ and the answer is YES. The simple one I took the picture of was up to around 200* in the time it took to make her talk. An enclosed oven style (made from a box) will get to 300*, and a commercial built one will get higher.