While there are expensive chemical treatments available at many of your larger hardware stores or online for cleaning a copper roof, you may be better off using a homemade solution plus a little time and elbow grease since commercial solutions could harm plants that may be growing around your home. Use a stiff non-metallic brush to brush on a solution of concentrated lemon juice and salt . If pure lemon juice and salt fail to work, the addition of white vinegar to the solution should do the trick. Remember to rinse with plain water (from a hose) when you are done. The following steps will help you to learn more about how to clean copper roofing.
Mix three parts of pure lemon juice to one part salt in your plastic bucket. Stir until all of the salt has dissolved.
Dip your stiff non-metallic brush into your lemon and salt solution and scrub on an inconspicuous part of your roof in order to judge the effectiveness of your solution. Really scrub with your brush. If the discoloration is not coming off completely try adding 1 cup of white vinegar to your solution. When cleaning, start at the highest point of your roof and work your way down.
Rinse your clean copper roof with water from your hose. Use a sufficient amount of water to remove all of the cleaning solution. Do not touch any part of your clean roof with your bare hands as the oils on your hands will react with the clean copper and quickly form a dark stain the size and shape of the portion of your skin which touched it.
Spray or roll a layer of clear lacquer on your clean copper roof if you wish to maintain the shinny copper look. Keep in mind that the lacquer will slightly darken the color of the copper as it dries.
Spray or roll on a special patina solution that is available at many of your larger hardware stores as well as over the Internet if you wish your copper roof to have a greenish patina. If choosing this option do not coat your copper roof with lacquer but instead follow the patina manufacturer's instructions for achieving a beautiful "old" copper look to your roof.