Do you really need it? If your current roof is less than 15 years old, it should have some life left in it unless it was installed poorly. Make sure it has been inspected thoroughly by someone who knows roofing before you take the plunge.

AJC File (ENLARGE)

Ridge vents provide ventilation to keep your home cooler.

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How long will it last? Different materials have different lifespans: metal is expensive, but can last 50 to 100 years. Asphalt composition shingles are much less expensive, but last 20 to 25 years. Asphalt shingles can now be made to resemble clay tiles or shake shingles. Real clay or slate roofs can last upward of 100 years.

How many layers? If you're going to live in your house for the full useful life of the new roof, tear off the old shingles and make sure decking is in good shape before putting on another roof. But if you plan to move in a few years and have just one layer, putting on a new layer of shingles would be much less expensive. The second layer won't last quite as long, but will be perfectly serviceable for many years.

What kind of ventilation? Adequate attic ventilation prolongs the life of your roof and keeps your home cooler. A system of soffit and ridge vents pulls air into the attic and pushes it out the roof of the house, cooling the area. If your attic is not already vented, build ventilation in when you have a new roof put on.

What about flashing? Make sure your contractor uses high-quality metal or synthetic flashing in valleys and around chimneys, skylights and vents that protrude through your roof. The best roofing material in the world will leak if not properly flashed.

Source: "My Home, My Money Pit," Tom Kraeutler and Leslie Segrete, KNACK Make it Easy/Globe Pequot Press. $22.95