Although it is best to hire a professional, cleaning a roof is not a hard job, but it is a dangerous one. Being that you already have a good understanding of the safety precautions that must be taken, the first thing that must be determined is the kind of staining that is actually on your roof. Is it tree sap, soot, mold, growth or what? The most common staining is a mold and growth discoloration. This type of cleaning is best done by using hot water under pressure and a combination cleaner. The chemical you use ought to be able to deal with organic stains, like Tough Stuff is able to do. It also should have a chlorinated additive so to kill the mold spores. Avoid using any kind of heavy chlorine alone, as it will damage to some metals, causing even worse staining, not to mention killing the vegetation that it falls on when dripping off of the roof. The procedure for cleaning the roof should be to start from the peak and work your way down, following a section at a time pattern. Professionals many times use a power broom so that they can work from the ground and avoid actually walking on the roof. However, you may not have this kind of equipment and therefore need to walk the roof. Be very careful not to damage the roof when walking on it. When power washing the roof, presoak with chemical at low pressure the section you are focusing on. After the presoak has had a few minutes to work, but before it dries, begin hot water power washing the roof using a variable pressure wand so that you can adjust the pressure and avoid damaging the roofing materials. Again, start from the peak using a 25 degree nozzle, about 3 to 12 inches from the surface. Make sure to aim the pressure down the roof. NEVER aim the pressure against the roof or up under the shingles, as this will surely cause roof damage. If you take your time and let the chemical and heat do most of the work, the pressure will then be only to push away the staining in an even manner. The result can make a stained roof look new again or at least all one color. Good luck and happy cleaning.