The large, red box oven that is pictured on this site was improvised using scrap wood and materials. The only thing that was purchased for the oven was the glass and the mirror.
Some have asked that I provide plans for such an oven. I am not a carpenter nor am I a draftsman so I have provided some drawings here to help the ambitious to improvise their own wooden solar oven. This will require that you have some basic building skills and some creativity. Scrounge the materials that you can; purchase what you can't scrounge! I have made suggestions for size of the oven which you can adust to suite your situation. Larger ovens are more powerful and efficient than smaller ones. It is also important not to make the oven too deep. Make it just as deep as to accomodate the cooking containers. (this has to do with minimizing shadows.) This is a large, heavy oven designed to be kept on the patio or yard. It is not very portable. Also, this type of oven will generally reach a maximum temperature of 250 to 275 degrees F, which is not as hot as ovens with multiple reflectors. However, these are perfect "slow cooking" temperatures" which many solar cooks prefer.
To use the box oven aim it at the sun, and tilt the reflector to focus the most sunlight into the inner box as possible. Put a dark cookie sheet on the floor of the oven, on top of the cookie sheet place a BBQ type of metal grate to elevate the cooking containers for air-flow. Use dark colored, covered containers such as "Granite Ware" glass amber ware (like Pyrex) or paint your own containers with BBQ or grill paint. Shiney cookware will work, but not nearly as well as dark cookware. You will want to make some kind of wooden prop to hold the glass cover up while adding or removing food from the solar oven. I made mine out a piece of 1x2 pine.
The Global Sun Oven is the best commercially made solar oven on the market. It gets up to 350 F, folds up for portability, weighs just 21 lbs, and will last a lifetime. I use the Sun Oven almost every day.
With this oven, as long as you have a clear, sunny day, you can cook in the middle of Winter!