Hi Andrew, I don't use a roller but I'll take a shot at this. How many coats you have to roll on would depend on the viscosity of your epoxy, the smoothness of the build up and your sanding techniques. The thickness doesn't build up very fast with a roller so you have to apply more coats as opposed to a brush. If you think there is any chance you might sand into the glass, add a few more coats. Last but not least, I read somewhere that when you think you have applied enough epoxy, add two or three more coats. Maybe someone with roller experience will offer more advice on this matter. Glen in Baie-St-Paul.