Looks like the 8' wall isn't load bearing and does not have much framing in that upper area.
I would look into enlarging the little louvered vent area and adding an awning above to keep rain out as well as opening up that part under the roof overhangs both on the front and back walls.
The inside construction of that area matters. If there are blocks between the rafters removing the board under won't do anything.....nor would drilling holes there.
Aart is right pics of the inside are needed.
I am wanting to see the inside of that wall so I can see the framing. Different sheds are built...well...differently.
The framing matters since suggestions can vary based on what is there to hook onto.
Pics of the inside end wall please.
We may suggest making big vents there and adding an awning to keep the rain out. Openings not under a soffit/roof overhang need protection from weather.
Instead of drilling holes under that overhang fully remove the board. You will need to add hardware cloth but it's more effective ventilation and is already protected from blowing rain.
Pics of the inside end wall please.
We may suggest making big vents there and adding an awning to keep the...