The last post showed the RTU from the exterior. Most can be identfified that way from the outside or from getting on the roof through a hatch.
But, what if the building is very large and tall? In some instances the make up of the building doesn’t allow for easy viewing of the roof top. The return air can be seen going into the RTU possibly indicating that there is additional load on the trusses.
Just be aware of what is above you. Some of these large buildings will have several of these on the roof just waiting to come crashing down. Follow the duct work and see where it goes. If you don’t see the full unit, it is likely on the roof.
In addition, look at the roof system. Who can identify what the added danger is?
When inside, look for this type of situation.
Take care and stay safe.