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.