Paint a shingled roof with roof coating paint. Depending on the original color of the shingles, you will need at least two coats of paint. The age and condition of the shingles will determine the success rate for painting.
Paint a metal roof with exterior metal roof paint. If the metal roof is currently a dark color, you will need to prime it first to get a true application of onyx black. Use at least two coats of paint, allowing each coat to dry completely.
Replace existing shingles with new black shingles. This will require removing all of the old shingles and laying down new roofing paper.
Cover the existing roof with black steel. Order steel roofing material in onyx black. This can be installed directly on top of shingles, or you can remove the old roofing material and lay the metal down on the structure of the roof.