I have always found portable signs to be the best, your customer knows you serve that area. The sign is there and if you choose good locations massive numbers of people pass your sign each day. Each day some look some don't so what. The ones that need you notice the sign. It should be done in a classy way not just Yellow letters on a black back drop. If you have the budget for it, a consultant is probably a good idea too. They have ideas your local roofer hero may not think of.