Here is my BBQ roaster - up and running and roasting great coffee!  PLEASE NOTE: This modified BBQ grill is for my own personal use and the pictures and descriptions below are not to be taken as instructions or advice in constructing your own grill roaster. Should you choose to do so, it is at your own risk as the grill and roasting drum / rod assembly reach 500+ degrees and can cause severe burns. That being said, by wearing gloves designed to withstand these temperatures, I have not harmed myself nor anticipate that I will do so.

I chose the 40,000 BTU, dual burner CharBroil for $169 from Home Depot.

The RK Roasting Drum fits nicely on the rotisserie rod and is held in place on the rod by the supplied collars.

Here is the gear motor I chose for the roaster. I got it from Surplus Center along with the coupler halves for under $60 delivered. This is a 30 RPM motor which is about as slow as I would want to go. RK Roasting Drums will provide a completely assembled 57 RPM motor, with mounting platform, on/off switch, couplers, instructions and support for $120. If you don't relish the prospect of this part of the project, that would be a good solution. Notice the less-than-professional workmanship to elevate and level the motor.

I wired in a regular light switch to easily turn the motor on and off with no plugging and unplugging of the power cord.

Closeup of the motor coupler halves with rubber "spider" between them. This connects the motor to the rotisserie rod. I still don't have the motor at the precise height, nor is it perfectly level yet, but the design of the coupler allows for this imperfection.

My very effective cooling system. When I dump the crackling 500+ degree beans into this 14" stainless steel sifter ($19.95 from a local restaurant supply store) and turn on the box fan below it ($10.50 from Target) - the beans are cooled within a minute or two. The fan is sitting face up on the arms of a PVC chair and the air blows up through the beans. This also helps blow away the remaining chaff.

While I happened to choose the RK Roasting Drum, there is another manufacturer who has also received praise for his product: Buzz Roasters. You can't go wrong with either of these.