1. Put fat lip down first. Short lip should cover the fat lip.
2. Screws should not be over tightened or under tightened. Over or under tightened screws could cause leaks or damage.
3. Goal should be to not to rely too much on caulk. It should be a fall back item or secondary use.
4. Metal should overhang the roof 1 and a half to 2 inches.
5. Pay close attention to penetrations in the roof such as a vent pipes.