Compost from the sky!!

A miracle!! The people next door are having their roof pressure washed!!!  The process has produced many wheelbarrow loads of moss and soil (as well as using huge quantities of water!!).  Of course I wasted no time in asking for the spoil.  Must be as good as peat as a garden ingredient?  The guy asked us to allow him to use our water supply as the flow from next door wasn't fast enough - I reluctantly agreed (all our water saving habits wiped out for a month or two!)  They are going to spray the roof with something to inhibit the growth if new moss - something I am also uneasy about and will keep our fungus growing logs covered for the day in case of over spray.