Put the same amount of coffee in the popper that the manufacturer recommends for popcorn. We put our popper by the sink so it blows chaff right into the basin. Turn the thing on. Wait another minute, then start to monitor beans closely for desired roast color by lifting out butter dish and looking into popping chamber, or, better yet, by smelling the smoke and listening to the crackling. Total time for a lighter roast should be around 4 minutes, full city roast around 5, and darker roasts closer to 6.5 minutes.
Roasts develop quickly, so be vigilant.
You want to pour the beans out of the popper when they are a tad lighter than the color you desire, since roasting continues until beans are cool. Agitate beans in metal collander with a big spoon or toss between 2 collanders until they are warm to your touch. You may need oven mitts for this. You may want to walk out to a porch to aid cooling. Warm, fresh roasted beans are wonderful, but the coffee attains its peak 4 to 24 hours after roasting.