Looks like a swamp cooler. Not sure if it is DYI, looks like some sheet metal was formed, unless it was a prefab plenum. At least the house doesn't have a 9/12 pitch!
Why are all these units on the roof out West? Small yards, theft, just the way business is done? You will not see this in the deep south. Even in hurricane and flood prone areas they are elevated, but not on the roof. I can understand a swamp cooler, but condensing units?
It's a poor man's cascade system. Pre-cool the air with the first and super-cool with the second?
A Veteran is a person, who at some point in their life, wrote a blank check payable to the United States of America for payment up to and including their life.
Gene Castagnetti-Director of the National Memorial Cemetery of the Pacific in Hawaii