I finally published my bee hotel for mason bees and it‘s running in a competition on printables
Edit:
The competition got cancelled because most of the models were not bee-friendly. Mine is!
It uses paper straws as nesting material and the backplate with the plugs for the straws is printed with PLA so that the bees won‘t chew on PETG.
German readers: If you want to now where I ordered my straws, feel free to ask.