There are many things to consider when thinking about hail resistance. First, a very strong point of metal roofing is that it will resist hail the same when it is many years old as it will when it is new. The UL 2218 Impact Resistance Test is performed on new roofing materials only. This concerns me because I know that there are non-metal products passing this test which would not pass the test if aged materials were tested. Next, in looking at the impact resistance of metal, things such as gauge, metal type, panel configuration, and surface coating all play a role. Additional, some of the shake and other facsimile products have optional foam backers for extra rigidity. Thicker metal can play a role in hail resistance. However, configuration of the panel plays a real tole. A heavily textured roof panel, as an example, can be formed out of thinner metal and be just as hail resistant as a smoother panel formed out of heavier metal. For answer to most of your questions, you need to make inquiries with specific manufacturers. Many metal roofs do come with hail warranties of one type or another. Most of them will not include cosmetic damage though because, obviously, any roof can only withstand so much in terms of hail size and impact. And, unfortunately, after a storm, there is rarely a way to quantify how severe the hail was. Many manufacturers will warrant their finishes against chipping due to hail. They will also often warrant against loss of impact resistance with age. You might also see whether the warranty provides materials only or materials and labor should a failure occur. Also, many of the smaller panel metal roofs can be repaired if hail damage does occur. Additionally, a heavier profiled product will actually “mask” some indentations caused by severe hail. Good luck. All Best.