If you're looking for a cost effective, durable roof for a home in Philadelphia, metal roofing is well worth considering. Though most Pennsylvania homes have roofs made of asphalt shingles, this is generally because of the low initial cost of installation rather than asphalt's overall performance. Well suited to the tough (and constantly changing) environmental demands of Philadelphia, metal roofing is an excellent choice for homeowners who want a low-maintenance, high quality material that will out perform and outlast many of the other options on the market today.
Benefits of Metal Roofing in Philadelphia
To really understand what makes a good roof, try and imagine what it would be like to stay outside, completely exposed to the elements. In Philadelphia, you'd be subjected to everything from triple degree heat to temperatures well below freezing, as well as torrential downpours and icy precipitation in all of its forms. Now, imagine doing that for a few decades; a roof's got a pretty hard job, and to do it right for any length of time, it needs to be strong, durable, and (especially in Philly) versatile.
Metal roofing handles all of these conditions with ease. It reflects heat when the sun beats down, pays little mind to drastic changes in temperature, and, of course, rain, sleet and snow slide right of it. It doesn't catch fire, it resists water, and when it comes to life expectancy, it is only surpassed by rock. If ever there was a material suited to Philadelphia, metal roofing is it.
Metal Roofing Installation
One of the nicest things about metal roofing is its lightweight. In most cases, it is light enough to install right on top of existing shingles without compromising the integrity of the structure. So, if you've got a roof that isn't up to par, you probably won't even have to remove anything to put a new metal roof on. Metal roofing can be found in both shingle form as well as in long panels of metal that are cut to fit your home. Each is installed differently, but the overall performance is very similar.
Once a metal roof is installed, the upkeep needed for it to function well is next to none. If you want your roof to be a specific color, factory painted metal is very fade resistant (and will often come with a good warranty, too).
Metal Roof Pricing
Probably the biggest reason why we don't see more metal roofing in Philadelphia is the price. Though typically much less expensive than tile or slate roofs, metal roofing is still initially more expensive than asphalt shingles (which are used on around 80% of American homes). Since remodeling or building is so expensive, especially in the city, most homeowners don't want to spend more than they really need to. Since asphalt is the standard, the extra money it takes to install metal roofing is often looked upon as unnecessary.
One thing to consider, however, is that a metal roof will generally outlast an asphalt roof and require fewer repairs over its lifetime. When you combine the longevity of metal roofing with its low-maintenance requirements, it could turn out to be the most cost effective option for your home. 
Jon Nunan is a freelance writer who draws on his experience in construction, ranging from landscaping to log home building, for his articles on home improvement.