Nothing! The only maintenance to the roof material itself is washing it a few times a year. Most standard household detergents combined with warm water are appropriate (avoid petroleum based solvents, harsh abrasives or citrus based products). Keep debris cleared to help avoid stains.
Note: While the rubber or TPO roof material itself is relatively maintenance free, any sealed openings in the roof do require periodic inspections & resealing, typically every 3-6 months. Please review the Owner’s Manual for more information on the Care & Maintenance of your RV.