Good paints to use on a metal roof contain substances called DTM (direct to metal) and Elastomeric. Oil-based paints are the best option and often contain the necessary components to ensure adhesion to the metal.
In addition to oil-based paints, there are specialty paints available through paint suppliers such as Sherwin-Williams. Uniflex and Neogard are two Sherwin-William paints that are fluid-based and recommended for use on metal.
In addition to choosing the right paint, a primer should be used on the metal roof. An oil-based primer is the best choice and ensures the oil-based paint goes on smoothly without leaving brush streaks.