Excella Requires Roof Cleaning

[Streamer1]

I took a look at 25' Excella recently. The interior was nice and the exterior was good up to the roof. Problem is this AS has been parked under some trees for about 3-4 years and has accumulated some greenish scuz on the exterior roof including the A/C unit and other items (i.e. vents, antennas, etc...) which are located on the roof also. My question: will a simple power wash take care of the scuz, leaves, dirt, twigs, etc... or do you think this will likely take several buckets of soap & water plus plenty of elbow grease? Since it is on the roof (not the easy place to work) should a pro be hired to clean it once and for all? Thanks all. BTW the roof is supposed to be white.