Cleaning the inside of coni roofs

[Applepicker]

Got a job with fancy white sofas directly underneath.  What's the best way to clean, is it off a step ladder with wet and dry scrim or squeegee? I figured squeegee would put black water on the sofas

 

[Nudel]

Cover up the sofas with a tarp and do them trad?

Maintenance cleans can be done with a stingray or similar if it's regular.