The only thing I can think of that can really damage the roof, is a pressure washer. I'm not sure why, but it is not recommended to use one on a RV. Must be something to do with the seams having caulk in them and the water can break those seals.
Yes i would be concerned about pressure washing also. Could get under caulking and cause a leak. Figure i will get out there in a day or so, and hook up to trailer and take it for a spin, and get back home, take some tide and give it a go. Jacked up one side of trailer today using Ubolt that holds the axle with a floor jack, one tire at a time to rotate tires to prevent flat spots. Not sure if this is correct way to jack up tires. Probably get a bottle jack and use frame from now on. I have read pros and cons about correct way to do this. Owners manual leaves a lot to be desired.