Can someone explain why in almost all commercial applications the A/C condensers are roof mounted.
When I inquire about mounting mine on low slope garage roof no one likes the idea for residential.

Is noise the main reason? Vibration to rest of house? Access? OR is it just that it's unusual?

Roof PROS: Shortest run for wiring & line set (20' or less) Unit would be less than 10' above indoor A-Coil. Shade - Unit would be shaded on N side of house. Damage - not likely to get hit by anything from kids etc.
CONS: Noise to neighbor a concern. Access - so the guy has to climb a ladder to 9' low slope roof. Weight of unit 225# - 6 extra 2x8 joists will easily hold 225#.
Other option is at least 80' run to S.Side of house. Expensive wiring & line set runs. Unit is 32x44" so blocks pathway and can get kicked by kids. No vibration on concrete pad but noise to that neighbor still a concern.
Unit rated 76 decibels (Scroll Compressor)
Any Advice, what am I missing? Thanks.

almost all commercial equipment is self contained. Home units are typically a split unit.
But to answer your question.
1. Weight of unit. Home roofs are not set up to hold that amount of weight in such a small area.
2. Access to service.
3. Codes, some towns do not allow for this.
4. Noise and vibration.
5. Appearance. People do not want to look at a unit on a roof. Again Codes.

Commercial systems are put on roof because of the way the building is designed. They are self contained and house both the outside unit (condensing system) and the inside fan system (evap system) Real estate is expensive on commercial properties, having a unit on the gound takes away from looks, car parking, and produces noise that tenents do not want near their windows.

Keep the unit on the ground. You can always pipe the line set under the ground along with wires, to an area that will not be damaged by kids.

Either way your going to spend money to put it in. Just on different materials.

Another suggestion would be to put a self contained unit in the attic with a side vent system. These oversized window type units have fans that can push air through ducts and are self contained. These units are often found in garage attic areas where they can be accessed for service.