the roof should have 4 drains in each corner ,they are small holes wd 40 is a lubricate used for hinges and other stuff
it works good to loosen debris as it bubbles and is about $2-3 for a can and it is everywhere 7/11 to walmart and beyond ,everywhere sells it.
To use it comes with a small pipe to attach to the nozzle then find the holes and spray them right inside in short bursts or it will bubble out into your face with the pressure if blocked.
i'll take a look in a minute to see where exactly they are