I have a 1550 psi one and it does a great job with plenty of power for washing the roof plus the front & rear caps, winter's green mold off. Without any need for soap or brush use.
I just did that a couple weeks ago. Next couple weeks I will do the sides. But will need to use some car soap & brush to help with that job.
I did add a extra 25' of hose to it so I didn't have to drag it up on the roof.