Painting new cedar shingles
Cedar shingles do not need paint. Without paint, they last a very long time with almost no maintenance.

As soon as you paint them, you are climbing on a maintenance treadmill of having to scrape and repaint them that you'd avoid by letting them attain a natural brown where dry, gray where wet appearance as they weather.

If you have issues with the natural color, dye or stain is a better approach than paint to changing it. The best approach is to let it be. The best way to stain or dye is to dip the shingle and let dry before putting it on the house.