Wanted to have easy access to my stacked storage boxes so I designed this stackable shelf. As you can see from the pictures, I scaled this to fit all of my different storage boxes. Fusion 360 file available so it's easy to scale it for your needs. Orientate so that the notch is down on shelf.

Optional hardware to connect shelves:

4mm screw holes on back to attach to a wall etc.

To combine them together, use m3x6 bolts and m3 nuts.

There's a vertical middle support on the model because it has thin edges and is a tall print. It should be easily removable after print. Circled red in the picture.

Recommend printing in PLA or PETG. With ABS it will be hard as the thin edges will curve very easily when cooling down. Also, no supports needed.