I just found Plannja's instructions, no triangle rule and various flashing etc., but they'll stay put until the roofer comes. It's not raining in while I tackle the main task for the summer, insulating the facade.
Thank you for the input!
Then I have a question, there is a luftspalt for roof ventilation near the wall. How do you prevent the underlagspapp from laying over and blocking it?
To manage the ventilation, I have installed some standing battens 25x38 on the wall the roof connects to (plank frame) and then a plywood on the battens. The plywood, therefore, abuts the raw sheathing. Roofing felt and sheet metal are pulled up on the plywood, about 250 mm.
I "only" have 28x70 spikregel outside the insulation to work with.
10mm gap and there is 18mm left for sheet metal, felt, and plywood.
Need to think a bit, but your solution looks smart.