Main question is how do I do the bottom
While I was training people who came to my survival camp, I used several sheets of glass for all 4 walls and the top also, sitting them all on a black piece of wood.
Another one was 3 ft x 3ft square with all flat black inside and a hinged all glass top. Aluminum was not used at all.
The funniest one I taught was just a tractor tire innertube inflated and laid flat on the ground over a black board and covered with a single glass plate.
You can bake bread in these ovens but cannot get a good crust tho. Use a bit more yeast or baking powder or mix.
Any soup, tea or stew which will get done at around 80°C/175°F will get done in these solar ovens.
You also need cast iron pots/pans or copper/stainless with them painted flat black also. All black parts except the glass cover.
Aluminum is good when using it in a reflector oven, but not for a good baker, just black.
Check youtube for lots of videos and get some ideas for your project too.