The roof is one of the most expensive, if not the most expensive system in a home. Most roofs last many years, if properly installed, and often can be repaired rather than replaced. An isolated leak usually can be repaired. The average life expectancy of a typical residential roof is 15 to 20 years. Homeowner maintenance includes cleaning the leaves and debris from the roof’s valleys and gutters. Debris in the valleys can cause water to wick under the shingles and cause damage to the interior of the roof. Clogged rain gutters can cause water to flow back under the shingles on the eaves and cause damage, regardless of the roofing material. The best way to preserve your roof is to stay off it and don't walk on the granules. Also, seasonal changes in the weather are usually the most destructive forces on a roof.
When looking for a roof contractor to come out and look at or replace your roof here's a few tips I recommend.
get three references and review their past work;
get at least three bids;
get a written contract, and don’t sign anything until you completely understand the terms;
pay 10% down or $1,000 whichever is less;
don’t let payments get ahead of the work;
don’t pay cash;
don’t make final payment until you’re satisfied with the job; and
don’t rush into repairs or be pressured into making an immediate decision.