Roof cleaning: when and by whom?

Hello,

for just under a year now we have been proud owners of a single-family house and are wondering how and when exactly one should take care of roof cleaning? Can you do it yourself or is it better to have a professional come?

What exactly do you want to clean there? And what kind of roof are you talking about?

I only know roof cleanings after 30 years ;)

... and I join toxicmolotow's question!