Here's a very simple panel store design for keeping plywood and other panel products neatly out of the way, safely.
The wood at the bottom is an off cut of a pine sleeper cut in half lengthwise. It is taller than the wall plate so the 2x4 off-cuts form a natural slope towards the wall. We then use some 19x42 pine strips to form a triangle which supports the panels and removes the loading from the wall itself (this design is self-supporting).
I then glued a strip of 3mm ply offcut along the bottom to provide a smooth surface to slide the panels in. My first panel is thick piece of ply which provides a sturdy surface for the rest of the panels to sit against.
The panels are stable in this configuration in that they won't tip over, even as you riffle through them, and they won't distort. For extra safety I put a spare octopus strap across the middle.