The best way to hang Christmas lights on a roof is to use a ladder to reach the height you need and then use hooks to attach the lights to the roof. Make sure the hooks are secure and the lights are evenly spaced for a beautiful display. You can also use clips or clips with suction cups to hold the lights in place. Whatever method you choose, make sure you have the proper equipment and safety precautions in place to prevent any accidents or injuries. Happy decorating!