When you say "Colorado," most people think of snow, skiing, and white-capped mountains. To the hvac engineer, these images also bring to mind concerns about reducing heat loss, improving thermal efficiency, and reducing the potential for condensation on air duct surfaces.
In addition, to the hvac system designer working in colder climates like Colorado, the thought of snow conjures up images of very wet roofs and ponding as the snow melts. That may be why system ductwork is normally not installed on rooftops in these regions, as it is in warmer states like California, Texas, and Nevada. So when The RMH Group (Lakewood, CO), a consulting engineering firm, decided to place ductwork on the rooftop of a Colorado prison, it departed from the prevalent engineering culture of the region.