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You all should know by now that I discourage DIY roof cleaning because of the hazards involved, but I know that some people will attempt to do it anyway.  So I wanted to throw together just a short list of safety products for roof cleaning that many of the pros use (yes it can get expensive to buy all this stuff but roofs with slippery chemicals on them are a recipe for disaster if precautions aren't taken (don't say I didn't warn you)).

1. Get some Cougar Paws - amazing traction.  The grip on these shoes is so good you'll feel like spiderman (or a cougar, I suppose).  In fact it is so slip-resistant that it can almost give you a false sense of security.  Wearing good shoes does not mean you can turn your brain off.
2. Wear jeans or long pants.  No matter what chemicals, products, or procedures you're using some of the stuff is bound to get on you, and better it land on denim than skin.  Of course whatever does get on your skin should be rinsed off immediately.
3. Wear latex gloves.  Cheap dish gloves from the grocery store will work fine.  Again this will help in keeping chem off your skin.
4. Wear goggles.  If most of this stuff is bad for your skin just imagine what it can do to your eyes.  If something does splash in your eyes flush them immediately! 
5. Wear a respirator.  You DO NOT want to get the fumes from this stuff in your lungs.  Trust me.  Make this a priority.  Getting dizzy from exposure 45 feet off the ground is playing with fire, not to mention the potential long-term effects of repeated close-range exposure.
6. Use a fiberglass ladder if possible to minimize the possibility of electrocution from bumping a power line.
7. You'd be wise to invest in a roof harness system if you're uncomfortable or unfamiliar with heights, ladders, or roofs in general.  Heck, everyone would be wise to use one.

Sounds like a lot, right?  Why not do yourself a favor and just hire a roof cleaning pro who already has the equipment and know-how to do it right.  Considering all the chemicals and gear you'd have to buy to do it yourself it would probably be cheaper to hire it out anyway, so why wouldn't you?  Even if you think that it might save you a few pennies to do it yourself, is it worth it when the potential risks include paralysis or death?  I want to say this one more time to make it perfectly clear:  chemicals or water on a roof will render it EXTREMELY SLIPPERY (think ice), so you better be prepared if you're a hard core DIY guy.