Hi Lucy..
Sunlight will kill it .
You can mix a little bleach with water, just a little chlorox mixed with water will do it.. Spray a lite mix on it and it will kill and bleach it out.
There is also a relatively 'safe' herbicide 'carmex' that can be mixed and used to kill moss, it is generally used in water ways to kill and control moss and algae...
With a little on your roof, occasionally spraying with bleach diluted, will keep it under control. You might also try giving it more sunlight... :smile:KennyV