A good commercial roofer will know exactly what needs to be done. Commercial applications require a different skill set from residential applications. The time factor is especially important. While homeowners may be okay with a two week job, a business is on a tighter schedule. Really, businesses cannot afford to take two or more weeks off for a roof job.
The materials used are very different as well. Instead of asphalt shingles, some use a special coating to cover the whole roof.
Waterproofing is especially important too. With all the valuable assets underneath, it is imperative that leaks do not occur.
Maintenance will need to be done on a regular basis too to keep everything in good order. For businesses, regular maintenance cannot be overlooked. Otherwise, it can lead to costly damages that may result from leaks.
Many businesses also have a very complicated system on their roofs. There could be smoke stacks, ventilation systems, roof entrances, external machinery, and maybe even skylights. Residences, on the other hand, may only have an ac unit and a chimney.
The technology used is also different. Commercial roofers keep up with all the latest developments in their field while residential roofers keep up with technology related to homes. Each is different.
What you use your building for can help you determine which to use. But if your business is a house, it may still be considered a residential job. The contractor will be able to tell you which it is.