Hey Dennis
I used a mix that goes like this (I got it from the Owens Corning site),
1 cup TSP, 1Gal. Bleach, 4Gal.Water
UPTO
1Cup TSP, 2 1/2 Cup Bleach, 2 1/2GAl. Bleach

I've used this several times and have great results with absolutley no harm to plants, But I also soak the ground and plants extra well just as a precautionairy measure.

A lot of times if the roof is real moldy it will get slick so be carefull, also I've heard that some folks dont even rinse the roof down, they let the rain do it for them. there also a place that will ship a product to you that is supposed to do a great job and is safe to the ******ment it runs about $16 a gal an gets mixed 7 to 1 if you like I can e-mail the phone number to you. hope this helps
Richard