Well if it's like a chuck roast with lots of marbled fat you want to take the roast to an internal temp around 200 and cook it low and slow. Smoker set to 225-250. That can take most of a day to cook. These roasts are for pulling not so much for slicing.
If it's a lean roast like top, bottom, or eye round you want to cook it however you like steak (rare, med-rare, medium, well). Rare being 125, med-rare 130-135, medium 140, well anything past that. Because these are lean roasts and you are cooking to lower temps they cook faster. I like to run my smoker at lower temps 180-200 to get more smoking time. These roast to get to an IT of 130-135 usually take 2-3 hours. They need to rest for 30-45 minutes wrapped in foil prior to slicing.