To prevent dead birds, leaves or other objects from entering the storm leader and causing a blockage and risking the building to collapse from the weight of water accumulation.
Also a dome type cover is the best choice as the beehive type even with debris around the base will still allow drainage from the top of the dome
Storm drainage piping.
Promenade LEVEL and 11/2 times the effective opening and roof top weather protection a DOME is strongly suggested
By placing a scupper 2"- 4" above the roof surface at the lowest point near the existing roof drain
do grants cover windows and roof
It should cover your roof for accidental damage, it will not cover a new roof if it needs replacing due to age.
Inside and or outside leaders
7
There is 32 sq ft in a 4 by 8 sheet of plywood. You would need at least 21 sheets to cover the roof.
Take your snake on the roof and clean the drain from the vent.
for a shingled roof you need 4in per footEnough pitch to allow water to flow to the internal leader (drain) or scupper or outside leader by gravity
A scupper allows water to exit the roof, usually into a gutter drain.
Then rain falls on a roof and if the roof works properly the rain will drain off of the structure.