My wife and kids made the box cookers, from the same link shown - they work... slowly. We want to build a BIG one, always how, always tracking the sun, ready to go, built into the side of the house.
Wish I could remember where I saw a pic of one, but it was bascially a big reflector outside the house, directing sunlight up into the bottom of an oven built into the side of the house. So long as the relfector wasn't covered, the oven was hot, and ready to go - no preheating, 350-450 an hour after the sun hits it.
Unfortunately, they ONLY had like 2 or 3 pics, one of the outside, and a couple inside - looked like a built in brick wall oven. There was nothing said on how they regulate temperature, how long it stayed hot after the sun went down or how well it worked. It did look well used, we think... or like someone stuck an old oven door on a brick fireplace.
I'd love to hear from ANYONE that knows anything about them - espically plans, schematics, how well they work, or DO they work.
Bill