Here is an area that many of you have probably never even seen let along done any maintenance, the roof. Now before we get started, if you rig does not have a ladder attached, DO NOT GET ON THE ROOF! No ladder means it is not designed to hold the weight of people. Even if your rig has a ladder, I would recommend using a standard ladder placed on the rig to gain access. Once on the roof please be very careful. They are slippery when wet, have all kinds of object designed to make you trip and the edges slant away from the center and you can easy fall off. It is best when you are on the roof to stay on your hands and knees. This way you have two advantages. One you are on four points of support. Two you are closure to the roof to do inspections and see issues.
Roof maintenance will include a cleaning, repairs of cracks and damage to the roof and installed fixtures from trees and other objects. Start with a good inspection of the seals and roofing material. Note the type of roof. How are you suppose to know the type of roof? Here is a video on how to determine the type of roof your RV might have. http://rv101.tv/2012/09/06/rv-101-how-to-determine-rv-rubber-roof-types/
Cleaning the roof only requires soap, water and a soft brush. No high pressure water hoses! I have seen them punch holes into the roof materials. As you are cleaning the roof, look for signs of peeling or loose caulking. These areas will need to be repaired. Also look for signs of water pooling. This could be an indication of soft or decaying material under the roof material. Note the area and inspect the inside of the rig for signs of water damage.
Once the roof is clean inspect all of the caulking, air conditioner(s) and vents. Use a flash light to check the vents for signs of nest or other blockage.
It is not a bad idea to do the inspection of the roof at least once a year. Please read my post on http://rv-inspection-service.com dealing with inspecting the roof.