First needed dimension is the thickness of the sheet — turns out the specification of 5mm is workable enough:
Thickness: 5mm
The magazines themselves are 10" x 12", and the stack is roughly 3.25" thick, so for this sort of box, we set it by the interior dimensions:
Width: 85mm (all dimensions are rounded up)
Depth: 260mm
Height: 310mm
We go to https://www.blockscad3d.com/editor/ and create variables for those dimensions:
We need one additional variable — Partspacing, and if we are going to have an angle to this, we should also allow specifying that slope — rather than specifying the angle directly, we can use the proportion / percentage at which the angle will begin along the front height, and end along the back top:
