Roof transition questions

I'm replacing my (1894 Victorian) wrap-around front porch roof, framing and all. On the end, it abuts a vertical wall. There are two issues to address (photo):

The decking has about a 1:4 slope to the end, but also a 2-3 degree
slope into the wall.

There is a ledge that extends to the left which aligns with the roof on the
edge, but is about 2" higher than the roof at the wall.

Both the roof and the ledge will be covered with the same shingles. How should I finish out the transition?

A previous roofer laid the shingles over felt only, and put "L" flashing on top of the shingles (a situation of which I was unaware). This created a funnel, sending the water down the inside of the wall, rotting the bottom beam.

Upon discovering the topology, I rebuilt this section once before by adding a small ramp about 8" deep and 2" high at the wall (photo). This reversed the slope at the wall and was even with the top of the ledge. One final small triangle of plywood tied together my ramp and the ledge to the decking. I finished it out with felt, flashing, and shingles, and it worked.

I believe there is a more proper way to do this, however. The final roof will be installed in the next few weeks by a real roofer but I need to get something in place temporarily in the mean time. I plan to use felt and flashing, but hold off on shingles. I'd like my temporary fix to be incorporated into the final roof as much as possible.

Any suggestions?