When you need to choose a roofing contractor to install your roof, you will have to find first. If you want something radical like install a green roof on your home, then you will also need to ask some questions like how much experience they have had doing this type of application. They may choose to send you a roofing questionnaire via email. You can also get professional steel covering in Ontario.
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Once you have three names of roofing contractors and the appointments are set you can sit back and relax until they make their visit. They will get up on the roof and walk it. And measure it. They may test some shingles.
They will look at the flashing and gutters and fascia and other roof parts for damage or mold or moss or other problems like broken flashing or cracked sealants if they can spot them.
When you have the three estimates you then need to compare. Make sure you are looking at similar roofing materials and any options so you can figure out if the estimates are for the same roof. If they appear to be different then call and ask questions. It is too late to ask questions after the work has started.
When you have compared the estimates and spoke with each contractor then find out just how long they estimate the job will take. Shorter is better. You are now on your way to a home roof installation.