Supply list. Three nesting pots. Brick to raise the structure. Insulation (coarse vermiculite or lava rock). Terra Cotta Clay Pots (Nesting Sizes, A, B, C can be 24in x 22in, 13in x 12in and 12x10 or similar. Just make sure pots B & C can rest rim to rim within pot A)

Using masonry bits, drill holes into the bottom of your largest and smallest pots. This is for air intake to stoke the convection currents. Make sure you drip water onto the pot as you drill to keep the blade/bit from getting too hot.

Holes.

Using a masonry disk or tile cutting bit on a dremel (or an angle grinder), cut the bottom off your middle sized pot. This will be the lid, as shown here. Again, as with the holes in the bottom, make sure you drip water on the pot as you cut. This will save your blade and reduce particulate matter in the air (dust, etc).

Ready to stack. Lift the largest pot off the ground with brick.

Place a second set of brick pieces inside the largest pot, to lift the next nesting pot up.

Place the smallest pot on the bricks inside the largest pot. 

Invert the middle sized pot over the smallest one inside the largest, outer pot. This will create an interior cylinder.

Put the lid on and fill the remaining space with lava rock or coarse vermiculite.

Add coals to the bottom, and light. Allow them to burn for at least 30 minutes before cooking. The oven reaches its best temperatures roughly an hour to and hour and a half after lighting the coals.

Remember to use oven mitts when handling the lid, it will be very hot.

Skewer veggies and shove them inside for a good roast.

Meat on skewers is perfect. The fat drips down and hits the coals, fueling a fragrant smoke.

Full picnic.