As you can see there is a large amount of moss and algae on the roof.

A shingle roof needs at least a 3/12 pitch. This means for every 12 inches the roof falls 3 inches. This is a 2/12 pitch and water is backing up under the shingles and causing wood rot and water damage to porch ceiling.

This dormer was build way to close to the edge of the roof. This section of roof that is no longer accessible should've been addressed before the dormer was built. The correct way to do this would have been to extend the roof to the edge of the dormer. Connecting the two, making this hollow area void. 

There is a lot of water entering The roof where the drip edge is due to it being install incorrectly.

Once a roof gets covered in algae it promotes the growth of moss.  That moss Grows where the shingles retain moisture, the edge of the shingle. The root system of the moss will begin to grow under the shingles allowing water to wick under the shingles and rust out the nails!