I own a roofing company and most people do not tip us. However we really appreciate when someone does tip. Some people buy us lunch while others give us cash. One homeowner made us lunch every day and one day while he and his wife were gone for the day they left the house unlocked so we could use the bathroom. They also stocked the fridge and told us to cook ourselves lunch. So we went out of our way to please these people in return. Tipping is not expected but we do take extra care of customers who do tip or bring us lunch or snacks. Use your own judgement. Do you like the guys and are they doing a good job and cleaning up nicely? If so, even a thank you is appreciated. Roofing is hard and dangerous and we like to know that we are apprecited.