Find two rectangular or square cardboard boxes. One should be able to fit inside the other. The inner box will delineate the cooking area and the energy given off by the cooker.
For an oven that is average sized oven, the area of the inner box should be 120 x 160 square inches, and the depth should be as deep as 9-12 inches. The smaller box should fit inside the other with 2-3-inches of space in all directions (The space will be filled with newspaper). Use larger boxes for a bigger oven.
Lay crumpled newspaper at the bed of the outer box, and then put the smaller box inside it. Insert a crumpled newspaper into the space that separates the sides of the two boxes.
Line the sides of the inside surface of the inner box with heavy-duty aluminum kitchen foil. You can use a non-toxic tape to hold the aluminum foil in place, or simply bend the ends of the foil over the top of the box. Never use materials which could release toxic fumes when heated such as Styrofoam or duct tape. Hold the edges of the foil and pull large wrinkles out. Using a clean cloth, rub on the foil outwards to smooth it.
Lay black construction paper on the bottom of the inner box. The black construction paper will absorb heat. Place a piece of cardboard on the outer box. Then, using a pencil, trace the figure of the outer box onto the cardboard with a pencil. Add 2 inches around the trace line, then cut along out (on that adjusted line) to make a reflector.
Using an aluminum foil, wrap that cardboard piece with aluminum foil. Remove any wrinkles or crumples. And use non-toxic tape or glue to secure the foil.
Staple have the reflector stapled to the outer back of the outer box. Position the oven with the box unfolded up and the aluminum reflector in front of the sun for optimum heat utilization. Lay in the solar oven. Put the food you intend to cook in the solar oven. A Use a dark baking tin will be used as a rack to , holding the food and catch boil-over.
Put some objects or rocks behind and in front of the oven to support it and prevent it from tipping over.