So the cost for the business should be minimal. The beauty of digital wireless is that its really an all or nothing type of thing. It takes a significant object to interfere with reception. Objects such as trees, walls, cars, etc that are in the direct line of sight between your antenna and the rooftop antenna will interfere. Normal walls and such should simply reduce signal strength.
Microwave transmitters are also a problem.
This includes your microwave oven and 2.4GHz cordless phones. See the next question for what you can do about interference. This is most prevalent for users who use a computer in their basement. However, it can also happen whenever there are a lot of obstructions between the antenna on the adapter and the antenna on the rooftop. It can also occur if you happen to have your antenna in a null spot.