To secure Christmas lights on a roof, you can use a variety of methods depending on the type of roof and the amount of weight you need to support. For example, you can use cable ties or plastic clips to attach the lights to the shingles, or you can use adhesive hooks to stick the lights to the roof surface. If you need to support a large amount of weight, such as an outdoor Christmas tree, you may need to use metal anchors to secure the lights to the roof structure.