Re: Mold in a shed roof
First thing you have to do is stop the leak. I'd recommend replacing the roof and any damaged materials before moving forward.
Once the envelop is sealed, then you can address the mold, which should be easily knocked back with a strong bleach solution. Also, surface mold is totally different from dryrot/wood decay, so once the moisture is gone, the mold should not come back once treated with bleach. You could use some disodiumoctoborate as a preventative, but in this instance I believe that to be overkill. Your mold issue is due to a roof leak, cure the leak, you get rid of the mold.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!