As a rule, commercial roofs are significantly different from residential roofs, so the business landlord/owner needs to hire a roofing company that is well acquainted with those differences. You want a high-quality company that has the experience and skill to deal with these unique challenges.
How are they different?
Commercial roofs are usually flat or have a very low slope with a larger square footage than most residential homes. Challenge: more opportunity for the ponding of water which can spell more opportunity for leaks and structural damage.
Commercial roofs have built in drainage systems. Challenge: the roofer needs to be aware of your precise system when replacing your new roof or help you upgrade if necessary. Roofers that ensure adequate drainage help avoid that dangerous ponding issue.
Commercial roofs require more structural strength to support the extra weight of the ventilation and heating/cooling equipment. Challenge: the roofer needs to keep this in mind when inspecting your entire structure. He should have an eye out for any degradation and be able to deal with it effectively before applying the new roof.
Commercial roofs, due to their flat design, endure a lot more abuse from exterior elements and therefore require material that is tougher and can withstand that abuse. Membrane materials (single-Ply, built up roofing (BUR) and modified bitumen(APP/SBS) are the options. Challenge: find the roofing company that has the expertise in applying these specialized materials. They need to be experienced in the proper welding of the material seams, and working around the common obstructions and parapets common to most commercial roofs.
Educating yourself now will make you a much more confident roofing consumer in the future.