I'm looking to paint roof white to help global warming

The roof is a good place to do things that reduce summer heat gain into the home. This helps to reduce A/C loads and costs. Most MRA member manufactures produce roofs that utilize coatings with reflective pigments. These pigments, even in dark colors, are good at reflecting away radiant heat. White is still most reflective but there are many dark colors available that meet Energy Star standards. Additionally, good attic ventilation is helpful for most homes, as is installing the roof with a dead airspace or thermal break. Some metal roofs, such as many of the metal shingles, have an integrated thermal break. In other cases, roofs can be installed on battens to create a thermal break.