I did my own tar and gravel roof. The supplies from Home Depot cost me about $200 per square foot. It would have probably cost more if I had skylights and a chimney to work around. I live in an area where materials don't cost as much as elsewhere.
The price is going to be dependent on material costs in your area, the square footage you will be covering and whether you are doing it yourself or a professional company is doing the job. It could costs anywhere from between $7500 to $12,000 if you have it done.
There are some roofing calculators available online where you can put all your specifics in and your area and get a rough estimate on how much 4,000 sq ft of commercial building would cost. Most roofers will do free estimates so you could also have 2 or 3 bid. posted by
Flutterbye (161)