Metal roofing is the most durable roofing available. Steel, aluminum and copper are metals widely used in the construction of commercial roofing systems. Metal roofing can be applied in sheets or standing seam. Standing seam roofing involves crimping metal sheets together (this system withstands thermal shock well because it allows for flexing). Depending on the metal used -- with steel being at the lower end of cost spectrum and copper on the higher end -- it can cost anywhere between $3 and $18 per square foot (as of February 2011) to install a metal roof.
Asphalt shingles are often used to create a commercial roofing system. Asphalt shingles are cheaper than metal but still quite efficient. Asphalt can cost anywhere between $1 and $4 for each square foot of professionally installed asphalt roofing (as of February 2011).
Coating an existing metal roof can increase the performance and life of the roof. Coatings act as an efficient weather barrier. There are many coatings consumers can apply to their existing roofing system to increase the life of the roof. Acrylic, silicone, butyl and polyurethane are roofing coating options for commercial roofs. Asphalt can also be smoothed over a roofing system to improve the roof's performance.