This is how I roasted coffee at the campground. The grill came with the campsite. The cast iron dutch oven sits on top. A white gas camp stove provides the heat.
Heat up the dutch oven. Add beans. Check every few minutes to observe the beans and to stir them with a big spoon. When roasted enough I dump them into a clean frying pan to cool. Fan the beans a bit to blow the chaff a way, let them cool and they are good to go. Flavor is enhanced if they have a chance to rest for 12 hours or so, but they will still make decent coffee right after roasting.