Rob,
I will post but its going to be a while for the build as I wil be out of town for a month.
The drum will be Carbon Steel 10" dia schedule 5 yes 5 its .133 thick at the wall. I will go with a rear perforated for the air flow to go thru the drum during roasting as most all do .
once I get the drum welded together I will sqaure the front and back to the shaft then take a skim cut of the OD to make sure its concentric. to the center line of the shaft.
By my estimates this will be a 2KG roaster or a little bigger

Bill

While laying out the roaster its aparent to me that you cound have a single footprint for a roaster with the ability to change the drum sizes from say 8" to 10" to 12" as long as you build it into the unit.
Mine from the front will be shaped like a tombstone being 24" high and 18" wide, it will have the vent pipe concealed as I do not like it sticking above the roaster.
over all length will be between 24 and 30" depending on the finished cabinet.

Ordered most of the components off ebay