I´ve remixed vfalendysh´ ITX-Case to fit a PSU underneath the board, for example a M2-ATX. Maybe you have to change the hole positions of the Motherboard-Holder to fit your PSU.
Things you need from the original file:
Also you need all files from me. I´ve also created the mirrored baseplate for you. You need to print the single segment of the motherboard holder.
Attention: You can only install the Motherboard upside-down, else you have to mirror the holder. I´ve did this because of better cooling for my board.
I will post pictures in a few days.