Roofing work is expensive and, unless you choose your contractor carefully, you can spend thousands of extra dollars for dismal results.

In its evaluations of area roofing companies, the nonprofit consumer group Delaware Valley Consumers' Checkbook magazine and found big differences in customer satisfaction. In its surveys of homeowners, 11 of the 46 companies Checkbook evaluated were rated "superior" overall by 90 percent or more of their surveyed customers.

On the other hand, substantial numbers of customers regretted their choices: Seven of the 46 companies received favorable ratings from fewer than 60 percent of their surveyed customers.

Checkbook's mystery shoppers - staff researchers working with local homeowners - also found huge price differences when they asked companies to bid on carefully specified re-roofing jobs.

For one of these jobs, price quotes ranged from $5,400 to $20,195, a difference of more than $14,000. For most jobs, the highest quote was more than double the lowest.

Checkbook found no price-quality relationship for roofing: Highly rated companies were just as likely to quote low prices as those that earned low marks for quality.

Here are Checkbook's rules to find a reliable roofer:

To identify top outfits, use Checkbook's ratings of area roofing contractors. Through a special arrangement, Inquirer readers can access Checkbook's roofer ratings for free through Nov. 28 by visiting the website below.

Because quotes for the same work often vary by 100 percent and by thousands of dollars, get several bids for your job.

There is no hard-and-fast rule on how many bids to get, but, in general, the larger the job, the more bids you should get.

If there are large differences between the first two or three bids, you should seek more. And get more bids when labor - not materials - constitutes a large part of the cost. All contractors pay about the same amount for materials, but hourly labor rates and productivity may vary substantially.

If you can't be present during the estimate, email your specifications in advance. Use estimators as your consultants, getting feedback from them to determine exactly what needs to be done. Then go back to them with the final description of what you want and invite them to bid on the work.

Before deciding on any contractor, ask for proof that the company is licensed and carries liability and workers' compensation insurance.

Get a copy of the warranty from the manufacturer of whatever roofing materials are used. Also, get a warranty on the roofer's work, ideally for five years or more; have the roofer write into your contract: "In addition to all other warranties, if roof leaks within five years or, better still, 10 years, except as a result of accidental damage, contractor will bear the cost of labor and materials to eliminate all leaks."

Get a fixed-price contract. Specify, using pictures or in words, exactly what roof areas are to be covered. Specify other details, such as whether old shingles are to be removed, whether flashings are to be replaced, who is responsible for cleaning up and hauling away debris, and exactly what types and weights of materials are to be used.

Although you should be able to obtain a binding contract at the estimate price, most roofers will insist on provisions for extra charges if they find damaged fascia, sheathing, or structural lumber. Most contracts state that required carpentry will be performed on a "per-foot" or "time-and-materials" basis. Make sure your contract states how charges will be computed, typically per-square-foot or per-linear-foot.

Avoid roofers that require big upfront payments. A 10 percent deposit to secure a spot on a company's schedule is reasonable, but beware the scammers who demand a large deposit to buy materials. Reputable contractors have credit accounts with their suppliers that grant them at least 30 days to pay.

Arrange to pay for all or almost all of the job after the work is complete. Most roofers allow customers to withhold all payments until the job is complete. Try to arrange to withhold at least a portion of the price until your roof has been tested by stormy weather.

Report problems immediately. If you can't arrive at a satisfactory resolution with the company, file a complaint with the state's consumer protection office.

The nonprofit Delaware Valley Consumers' Checkbook magazine and rate service companies and professionals. See ratings of 46 area roofing companies free of charge until Nov. 28 at