I am sure you can search the Internet and find many articles about the qualifications you should look for when hiring a roofer, but most of what you read will be only partly correct. It is standard fare to say that you should check a roofer's licenses, insurance, and references, but will a cursory investigation determine that the roofer is qualified? I doubt it. In order to get a better understanding of the roofer's status you must look deeper into these three areas, not just glance at the documents he leaves with his estimate.
Licenses are probably the easiest thing to check if you do a bit of homework. Make a few calls or Internet checks to determine which licenses, if any, are required. There are many roofing organizations throughout the US which will have a list of the necessary licenses. If you can not find such an organization for your area you can contact the National Roofing Contractors Association and they will be able to help.
Insurance is a bit harder to check and claims a defect investigation. Again, in some states no insurance is required, and in some only partial coverage is needed, so you need to determine the particular requirements for you state.
There are basically two types of insurance, workers' compensation and liability insurance. Almost all states require "workers' comp" but some states, like Texas, do not. If your state requires workers' compensation insurance then you should make the necessary inquiries to be sure that you will be covered. Ask the contractor for proof of coverage and make a few calls to verify he is covered.
When talking about workers 'compensation insurance, there is one thing to remember – the homeowner is not covered by workers' compensation. Workers' compensation covers the worker if he gets injured and protects the contractor from lawsuits by his workers, but this coverage does not necessarily extend to the homeowner. To be on the safe side, you can have all the workers and contractors sign a "hold harmless" agreement which states that they will not sue you in case of injury or death. This still will not protect you one hundred percent, but is an added layer of protection.
Liability insurance is another matter. There are many contractors who claim they have liability coverage but in fact they just have a piece of paper. The only way to be certain your contractor does, indeed, carry liability insurance is to call the roofer's agent directly and ask him to send you proof of coverage. You should also check to see how high the deductible is and to make sure the contractor is financially able to meet the deductible; sometimes this deductible can be thousands of dollars.
Checking references is probably the most difficult of the three items to verify. It is doubtful that the contractor will give you a list of negative references so you have to be careful. Another problem is that the references probably do not really know a lot about roofing so the most they can tell you is if the contractor was reliable and took care not to damage their property. However, it is still best to call four or five of the names you are given to get an idea of the contractor's reputation. You never know what you will learn.
Take time when hiring a roofer to make sure you have done a thorough investigation. The time to learn about your contractor is before the job starts, not after a problem arises.