To prevent rust, it's coated in zinc (galvanized), a zinc-aluminum alloy (Galvalume, shown), or blended with chrome (stainless steel). Available in seamless or sections; joints should be soldered. Galvanized steel lasts eight to 15 years before it rusts; Galvalume has a 25-year warranty; stainless steel never rusts. Choose 26 gauge or thicker.
Cost: About $2 to $8 per foot for galvanized, $2 to $4 for Galvalume, $4.50 to $12 for stainless