If you fall off a single storey roof you will most likely be seriously injured or dead. If you fall off a double storey roof you will definitely seriously or more likely dead. Evaporative cooling on roofs will need to be services, and they will break down. When this happens somebody will need to access the unit to repair it. You cannot get up on a roof if it is wet or too hot. This can be time consuming, require multiple service technicians, anchor points, ropes and harnesses and as a result the cost can be seemingly expensive.