I would suggest using the seamless type metal roofing. I put a metal roof on about 15 years ago and over time a few of the screws backed out, making a leak. It seems that this is a common problem.
I'm not sure what you are calling seamless. My metal roof will have standing seams running down the slope, but each sheet will be one continuous piece running from the top to the bottom on the slope. So each piece will be 24' long.
