Designed to fix 8.5" x 11" paper.  Storage area is extended to ~9.5" x 12" and it ~5.5" high.  Sides are slanted at 3 degree which also makes them stackable when empty.

Printed in PETG, 2 walls, 3 bottom/top shells, 15% infill.  Any filament should work nicely

No supports required!

Original design in OnShape:  https://cad.onshape.com/documents/a7885cd4ab1b3da15bea1361/w/3c9aee3343882312d4d5f6a5/e/029c9f79f60c9563c250cd77