|My moss solution...|
I finally bought one large box of baking soda about a year and a half ago and got out on the roof of the garage. The two sentence tip really did not elaborate on how you used it: Must the surface be dry?, Should you dilute it with water? So I figured I would start with the one box and see what happened. A dry roof just seemed better from a safety perspective so I went out there on a dry day and just sprinkled the baking soda directly from the box. It certainly was not instant death, but the fact that it was no longer green was victory enough for me.