Cut a large metal drum in half vertically with a jigsaw (e.g. oil drum).
Clean the inside of the half-drum thoroughly with a de-greasing soap (use a scrub brush).
Size and cut three pieces of sheet metal to contour to the insides of the half-drum. You need one large rectangle for the curved interior and two half-circles for the end pieces.
Attach the sheet metal to the inside of the drum.
Paint the inside of the oven with a reflective paint rated for barbecues.
Create a continuous metal lip around three of the four top edges of the oven. This will hold the glass top (which you will slide in and out through the fourth, open side) in place.
Flip the half-drum over and apply spray-on insulation to the outside walls.
Attach a base to the bottom of the oven (ex. a piece of wood, a square aluminium frame with wheels, etc.).
Drill drainage holes in the bottom of the oven. This will allow liquefied steam that drips down the sides to escape the oven.
Slide a custom-sized sheet of tempered glass into the metal lip.
Insert a magnetic thermometer.
Place a thin aluminium grill along the bottom (optional).
Test your oven’s heat capacity on a sunny day. Though you can reasonably expect a max heat of between 250 and 350oF (90 and 175oC) depends on the size, materials, insulation and weather.
Method 3: Solar Veggie Steamer
Use 2 cardboard boxes with 1 inch (2.5 cm) different dimensions, 5 cardboard panels, one vastly larger than the rest, Styrofoam, transparent wrap, aluminium foil, black craft foam, black Tupperware (with lid), water, your favourite veggie, glue, and 5 sturdy sticks.
Place the large box onto the large cardboard panel, glue in place. Place the smaller box inside the larger box, glue in place. Trim off any difference in height.
Line the empty space in between the 2 boxes with Styrofoam (don't use glue). Line the inside of the small box with 2 or 3 layers of the black craft foam, then glue together. Completely line 4 cardboard panels with the foil and glue the foil to the cardboard. Try to avoid creasing the foil.
Glue the panels at a 45 degree angle to the box.
Cut a rectangular hole just large enough to slip the Tupperware through on one side of the cooker.
Take the transparent wrap and stretch it over the entire mouth of the solar cooker.
Google the "Woodgas" camping stove - it burns pretty much any dry woody leafy fuel pretty smokelessly, but has to be outdoors. It works with a small battery-assisted fan. Allegedly designed to help third-world countries by minimising smoke pollution. I have one and it is very effective and leaves minimal ash. However the fuel load is fixed (although the stove comes in various sizes/loads). Mine works for 10-15 minutes and its done. Stop and reload. Great for fry ups while camping. Works when there is no sun too !