It depends on the type of roll you're baking. If you're making a sweet, enriched dough like cinnamon rolls, then brushing the dough with butter before baking will create a softer, richer texture and flavor. If you're making a savory roll like dinner rolls or crescent rolls, then brushing with butter after baking will give them a nice glossy finish and an extra layer of flavor. In general, it's best to brush your rolls with melted butter just before baking so that the butter melts into the dough as it bakes. This will help keep your rolls moist and flavorful. If you brush them with cold butter before baking, it can slow down the rising process and make your rolls dense. No matter which method you use, always be sure to use unsalted butter for best results. Salted butter can make your rolls too salty if used in excess.