As far as walking on the roof without falling through a few sheets of plywood or planks horizontal will work.
You then need to determine how the roof is tied into the stucco wall. It should be turned up behind the stucco a few inches. If the porch was added on after the stucco was done the metal might just be butted to the house and be relying on that bead if caulk to keep the water out. The black stains on the bottom of the stucco indicate that it is wicking some water up which is not good.
From the caIulk on the screws it looks like the roof has been a problem before. It might be time for a new roof. If the metal just butts to the stucco the only thing you can do is cut out all of the old caulk, clean the stucco, and apply new caulk every few years. I would suggest having a good roofer take a look. Other options might be installing a flange a few inches up the wall and out onto the roof and then cutting a counter flashing into the stucco.