Metal roofing comes as panels or tiles. Panels are manufactured in lengths up to 20 feet long so they can span from the eaves to the ridge without horizontal joints. The panels are joined along their edges with "standing seams" that prevent water penetration and give the roof its characteristic ridges. Once associated with mountain getaways and high-end architectural homes, standing-seam metal roofing has become an increasingly popular option for other styles of houses as well. Because it features a factory-paint finish, it is available in a variety of striking colors.