A hell of a lot of roof but put it on the ledge for better airflow.
Thats just about as bad as the one I saw on a rooftop. Janitrol package heatpump setting four concrete blocks high. Three foot from edge. Duct in with ductboard through old curb. I stopped the other tech. from pushing on it to see if it would fall.
This was on top of a four story building. Now I see how the other company beat our price by a thousand dollars.