IMPORTANT: You need to have some basic leatherworking skills to complete this project.
EDIT: Version 2 of this deck box is available here https://www.thingiverse.com/thing:3436053
This box can hold up to 75 double sleeved cards, with a bit of room for a token or two. It's tall enough to fit dragon shield sleeves, and these are the tallest of all AFAIK.
Just print both pieces at 200-300 micron LH. The magnet holes on the lid should face upward.
Once printed, place the box on a piece of leather and trace the outline and stitch holes. Trim the leather, poke all of the holes and cut stitch grooves in between them. Repeat the same for the lid.
Take the leather off and thin the inside where the leather folds. Repeat the same for the lid flap.
Apply dye next. For a more distressed look, wet the leather a bit at random spots, wait a few minutes, then apply your dye. Finally, smooth all edges and apply leather oil as needed.
Before stitching the box together, cut a small piece of leather and stitch it to the inside of the lid. This will prevent your cards from moving or slipping while in the box. I've accommodated a 3-4mm tolerance in the box design.
The lid is held together with 6mm magnets. You need 6mm tall ones for the box and 2mm for the lid. All holes are slightly deeper and that should be enough for a drop of epoxy or E6000.
I'm no CAD and leatherworking expert and this was my first go at using both in a project. Any feedback and/or tips are highly welcome!