The Better Business Bureau says it is one of the biggest scams being perpetrated on homeowners, according to its new Scam Tracker Annual Risk Report.

A man knocks on your door and claims to have leftover roofing materials from another job nearby. He then offers to fix yours for nothing.

If this sounds too good to be true, it is.

The scammer — who loves to show up in those neighborhoods ravaged by storms — takes your money without doing the promised work — or very little of it.

Now that you know what to look for, you can use these tips to choose a reputable contractor to repair or replace your roof if needed.

• Ensure they’re insured. Contractors must carry insurance for all employees and subcontractors — and provide a copy for your inspection. That’s non-negotiable, so insist upon it.

• Run if they suggest ducking your deductible. If the contractor claims to be able to handle a storm-related repair, without you having to pay your required insurance deductible, that’s insurance fraud — and something you don’t want to be a part of.

• Run even faster if they ask for more money down. It’s reasonable for contractors to request a modest down payment before work begins (consider it “earnest money”), but if the figure exceeds 20 percent of the bill’s projected total cost — say, 50, or even 75 percent — it should set off a red flag.

• Know your contractor. When it comes to peace of mind, hiring a contractor who is a member of a reputable roofing manufacturer’s contractor program is helpful. GAF, North America’s largest roofing manufacturer, for example, is exceptionally strict about who it designates as its highest-ranking “Master Elite Contractor” — less than 2 percent of roofing contractors have qualified — and you can find one in your area through a quick search on gaf.com.

“We have a full vetting process we go through to determine whether they’re the right contractors to put in our program, like making sure they’re licensed where required, insured, and have a history of installing roofs in the local community,” says Jim Slauson, GAF vice president of certification program and services.

• Communication skills matter. A knowledgeable contractor worth their salt will offer a range of roofing shingle and accessory options by price, style, and color.