My in-laws had a metal roof and when their house burned down, the fire chief told us 2 interesting things that he wished people understood about metal roofing. (Too late for my in-law, of course.)
1) it's a nightmare for firefighters. They can't just hack into it with an axe and fight the fire from above. In fact, there's little they can do with a metal roof. The fire will have to be fought from the ground, limiting their options.
2) Firefighters are reluctant to spend too much time inside a metal roofed home. As the structure weakens, the roof weight can easily cause the entire structure to buckle and trap them inside. This happens with regular roofs, as well, but not as quickly and not all at once. A metal roof tends to come down all at once.
Related to number 2: When the structure buckles, the roof will "pancake" your house to the ground, meaning that anything that might have been recoverable will now sit underneath that roof and bake for days. When a regular house burns, you'll often see part of the structure still standing, and maybe some things are still salvageable. But by the time that roof sits on top of the flattened pile of debris for several days, all you've got is ash.
He said that doesn't mean that people shouldn't get metal roofing, he just wished people better understood that if it comes to a fire, the fire dept. is limited in what they can do and you will likely have nothing left.