Well here is the fire box for my wood burning raku kiln. This picture does not show the roof but the roof will be a piece of 1/4 inch stainless steel plate. I found it in a scrap pile and it happened to fit pretty well. I'll try it and see how it works.
Anyway, the box is made out of hard fire brick laid on a base of cinder block, which sits upon a slab of concrete. I used half in rebar for the grate. I've decided to add a few more bars spaced about two inches apart. Next step is to build the firing chamber. Stay tuned.