You'd think someone with the smarts to build that would at least learn about roasting coffee. Does not compute Will Robinson.
I don't get the use of a large diameter drum? Seems like you'd have to run it a 20 - 30 RPM to keep the beans agitated. And a clothes dryer drum that already has vanes would seem a better choice.
But if you put a shroud around it to contain the heat and sized the burner properly, that'd be a good start on a 2k roaster.