Your roofer’s work and its financial responsibility should be your biggest concerns. No job is a bargain if your roof leaks, looks terrible, or is never installed. But once you have identified roofers that measure up on quality factors, price becomes critical.

Contract to have roofing work done on a fixed-price basis, following an estimate.

Our undercover shoppers worked with three homeowners to get bids on roofing jobs. As illustrated below, the roofer-to-roofer price differences on the same job were striking. For one project, prices ranged from $11,203 to $24,914—a difference of $13,711. For another job, quotes ranged from $9,299 to $18,361—a difference of $9,062. For the third, prices ranged from $12,000 to $21,000—a difference of $9,000.

So get at least three bids from companies rated high for quality. Don’t assume a low bid signifies lousy work: For each of these three jobs, our shoppers received low prices from top-rated outfits. And don’t get bids only from companies that quoted low prices to us. Our experience with roofing bids is that there’s often no consistency: Contractors charge high prices for some jobs and low ones for others.

Here are some guidelines:

If you know you need a new roof, and yours is fully visible via Google Maps’ satellite view option, many roofers will use software to supply estimates without needing to inspect in person. If you want to meet in-person with a roofer to determine whether you need a new roof or just a repair, you still usually don’t need to be present when estimators arrive, unless you need to point out water damage inside your house.

Get more bids on larger jobs. A 20 percent saving on a $750 repair job is just $150, but if you can save 20 percent on a $20,000 job, that’s $4,000.

Get additional bids if there are large differences between the first two or three bids.

Get more bids on jobs when labor, rather than materials, comprises a large portion of costs. Contractors pay roughly the same amount for materials, but there may be significant differences in their hourly rates for labor and how much their workers accomplish per hour.

For small repair jobs, some contractors work on a time-and-materials basis. If possible, avoid this arrangement; you’re much safer with a fixed-price contract. But if you must pay by the hour, ascertain the hourly labor rate, how many workers it includes, the minimum charge, whether you’ll be charged for travel time, and how partial hours are rounded.