Shed Roof is Black and Has Water Damage

The black is bad get a screwdriver and see if the plywood is compromised. Push on the screwdriver and if it goes into the wood 1/8 “ or further the wood needs to be replaced. If it is still solid I would use a very strong solution of hydrogen peroxide and water 5-8% and saturate all the fungus areas a second treatment may be needed but this will kill the surface fungus that will break down the plywood.

Note 8% hydrogen peroxide will bleach just about anything including your hair so use ppe. It can be applied with a paint roller or sponge, at this strength I would not spray it as I do with 3-4%.

AAA. Always add acid to water to reduce the exothermic reaction when diluting concentrated hydrogen peroxide with water.