Step 1: Assemble the roaster
I purchased my basket as well as different varieties of green coffee beans from Sweet Maria's. http://www.sweetmarias.com/sweetmarias/coffee-roasters/roasting-supplies/behmor-small-grid-drum.html
Next you'll need to assemble some sort of drive shaft out of whatever parts that will allow you to attach your cordless drill to the roasting basket. I started digging around in my toolbox and found a 1/4" to 3/8" socket wrench adapter, fitted to a 3/8" socket wrench extender. Then found a 12mm socket that happens to fit the other end of the socket wrench extender and finally a socket to drill adapter to complete the driveshaft. You could get by with just a 1/4" socket wrench extender and attach it directly to your drill, but I did not have one.
You'll need a cordless or corded drill or whatever motor you can find that will spin the basket at about 1 revolution per second. Roasting coffee takes about 20 minutes so you will want some sort of clamp that you can attach to the drill to pull and hold the trigger. In my case I also need a couple of blocks of wood to support the drill at the proper height of the barbecue rotisserie brackets.
Next you need to prepare your barbecue grill. I think a gas grill is going to be the best bet here as I don't think you'll want a lot of smoke flavor in your coffee. You'll also need one that is setup with a rotisserie function or at least has the brackets for one. The motor that is used for rotisserie chickens is much to slow for roasting the coffee so don't bother trying to use it. Our grill came with some extra brackets that I use in the center of the grill to hold the roasting basket. I just shove them in between the two halves of the grill and hold it down with the weight of one of the grill grates. (see photo above) If you need extra brackets, you can make them or buy something like this.. http://www.charbroil.com/rotisserie-bracket-handle-side.html You'll also need to remove the grills under the burner that you're using to allow the roasting basket to fit.
Once you've assembled all your parts, you will want to clean up your grill as much as possible. I'm guessing chicken flavored coffee isn't going to be the next best thing :) Our grill has a "Clean" setting which runs the burners as hot as it goes and cooks everything to dust. I clean it up and run it on high until there is no more smoke coming out of the grill.
As always, please be careful and read all the safety requirements for the operation of your particular gas grill. The coffee you are going to roast is also going to finish some ware around 400 degrees or higher so please wear proper clothing, oven mitts etc. Also be aware if you forget about your coffee and cook it to oblivion, it could actually catch fire so please keep a close eye on things.