I too have thought this idea over and my thoughts were to build the structure from congrete block then line with fire brick. Leaving a hole in the front big enough to shovel coals into it and using corrugated metal sheets to cover the top and the opening in the side. And have a grate made or make a grate for it.
This is a real good watch if you havent seen it.
Custom 250 gal drum cooker,Weber OTG,Maverick ET-73,Covert Black Thermapen