I recently went through this as we put a new roof on the house we purchased in September.
We were weighing metal vs shingle. The quote for my Owens Corning dimensional shingle (40yr, with a grain of salt) was $7500 and the metal roof was $10,000.
No brainer right, go with the metal. Well did some more digging and not all metal roofs are created equal.
The $10k offer was a 29gauge (i believe) thick metal with exposed fasteners (think close to dryer duct thickness !!!). Basically a barn roof. Take a close look at the wind resistance to the roof you look at. If you get ANY wind in a storm those fasteners will pull right through the metal and there goes your roof.
After looking at a proper standing seam metal roof with 26 gauge, it was over $20k
I figure at worse case i'll put 2 40 yr roofs on this house (unless storm damage), and then i'll be dead and my kids can worry about it. Still cheaper than a proper metal roof.