I have a standing seam metal roof over the shingles on my house. Can't tell you how old it is, but it's there in the 1970's pictures of the house.
It's a standing seam design, so there are no issues with nails popping or rubber gaskets failing.
It's noisy in the rain. Be aware of that. I like the sound myself, but not everyone does.
Mine can be noisy in the wind, because the house is old and the roof surfaces aren't perfectly flat. So the metal panels can buzz and rattle some when the wind is strong and just right. Just consider that and look at your roof and see how flat and true it is.
