Metal roofs are becoming very popular here. We live in what the insurance companies call the hail county capitol of the country as there is more $ paid in hail claims here than any other county in the us.
We are waiting for a good hail storm so we can get the adjuster out and look at our asphalt roof. Almost no one pays for their own roof here as the roofing companies keep their prices very high because insurance companies pay to reproof houses here cause of hail and storm damage.
My shop is a steel R - panel building insulated with the roll fiberglass with plastic on the inside. When it rains I can hear the rain but it isn't bad at all. Here it rains so little anymore that hearing the rain is a good thing.
Loml's past house had a standing seam roof and no issues at all. Asphalt roofing may last 10 years may last 2 just depends on the weather. The big benefit of metal roofs here is reducing heat gain. Anything you can do to keep heat out is a good thing.
I like the idea of the pex up there but... I'd have to hook it to a big radiator and use it to pull heat away from the house.
One issue with metal roofs is that regular r - panel will need cleaning if you have trees. I have to scrub the end of my shop roof where the tree drips on it. It puts a black gunk on it that absorbs heat. The galvalum isn't nearly as bad as it seems to self clean.
Standing seam or flat seam are the best for a house but r panel is done allot because it's cheaper. I prefer standing myself as it and flat have no visible fasteners. But r panel is much heavier material.
If you do plan to go steel look up the local metal building suppliers. The one here will come out measure the house and give a materials quote for free and most everything comes precut. The shop gets the steel on rolls and runs it through a roll former.
Steel Buildings, Metal Buildings, Metal Roofing | Mueller, Inc is who we have here.