Arrange a layer of graham crackers on the bottom of an 8-inch foil pan. Sprinkle the marshmallows, Rolo, and chocolate chips on top. If you don't need all the graham crackers to cover the bottom, you can assemble the nachos in layers.
Cover the foil pan and place it over hot coals (not direct flame!). Let it cook until the marshmallows and chocolate are beginning to melt, about 10 minutes. The cooking time will depend on how close your pan is to the heat.
Remove from the heat, uncover, and dig in!
Notes
Keep the heat low--Don't cook over direct flame or you will burn the chocolate. Steady heat from hot coals works best.
Doubling the recipe--To double the recipe, use a 9-by-13-inch pan, or two 8-inch square pans.