Here's how I do it, I have 12 out there working away, (well 11 really #1 sucked and I cannibalized it for parts) 9 x 55 gallon, 1 dead 55 gallon, 2 x 85 gallon!
Shopping list1 x open top 55 gallon drum, (if it has a colored liner once you have the holes drilled, burn the heck out of the barrel, use cardboard or cardboard and wood, get the whole thing as hot as you can, or you can use a weed burner, nasty fumes DON't breath them), better to find unlined food grade drums if you can.
Use the charcoal grate out of a Weber kettle, 17.5" diameter, wrapped in 60" x 10" of #9 expanded metal.
3 x 1/2" x 1.75" stainless nuts bolts and washers.
3 x 1 1/2" U bolts, with plates and nuts, (Don't use Nyloc nuts, use standard nuts, I use galvanized U bolts and weed burner the heck out of them... WARNING don't breath the vapors though).
3 x 15 Oz Tomato sauce cans, topped and tailed.
2 x 22.5" grill grates.
3 x Cheap metal handles from Lowe's or Home Depot.
1 x Turkey fryer thermometer (WalMart $5.00).
Fridge magnets or 1" round rare earth magnets, Lowe's or Home Depot.
ToolsTape measure.
1 x 1/8" drill bit.
1 x 1/2" drill bit.
1 x 3/4" step drill bit.
1 x electric drill.
1 x sharpie.
Wrenches to match the nuts & bolts
1 pair heavy work gloves
Weed burner.
Build instructionsTurn drum upside down, measure 2.5" down from the bottom lip.
I like 6 evenly spaced holes, some like 3 some like 4, pick what you like, as once you have it running at temperature you will mostly only be controlling it with 1 hole. I like the 6 holes for a couple of reasons, 1) symmetry the 6 holes works well with the 3 grate supports. 2) You can alter the choice of hole to use in blustery or windy days. 3) You regulate the intake on the side away form the wind, with 6 holes, I twice as much choice as with 3 holes.
Drill the pilot hole with the 1/8" drill bit, then run them out to 3/4" with the step drill, (I find the 1/2" holes a little small to control the pit with only one hole, and you don't need to go as big as an inch).
Eyeball the position 180
Don't know where the rest went, so here's a link to the full version
http://www.thesmokering.com/forum/viewtopic.php?t=49419