I've been reading up on these Oil Drum Smokers, affectionately called UDS.
The idea is that you take 55 gallon drum, burn the stuff out of the inside, and put pipe fittings into the sides at low level. Then you can use control valves to adjust airflow to the basket of charcoal you put into it. I've seen reports of 12 hour burns at 250 degrees on one charcoal basket, add wet smoking wood and you can smoke 2 or 3 grill racks of whatever you want, seen 4-6 racks of ribs in a single smoker.
I'm in the process of chasing leads for the barrel itself, before pricing hardware etc.
Seems fairly doable, my dad has the experience and tools from 20 years of industrial maintenance, so I've got backup. I'll try and post pics if I get it done and remember to photo the process.
Any tried making a smoker/grill before?