1-Shot/Chromatic or Ronan bulletin paints and roller it on. Some use foam rollers while others use nap. Make sure you clean the board and get all the dirt and grime off the board before you start. Three coats should do it. Some will say you need to primer first, while others will say to get pre-primed. However, if you're going to get half it pre-painted, you might as well get RTG panels. That's panels totally prepainted from the factory. You just have to touch up the edges. No muss, no mess and you're ready to apply vinyl immediately.
Good Luck.