I've designed a shelf to raise my coffe equipment. I've used a pine plank, 200mm width, 20mm height and fits perfectly. It is very stable and can be done in any length size. The example I have is a 120cm plank.

If requested, I can make another bracket to put in the middle to give more support.

Printed in PETG, more than enought for the load.

You can continue to stack them up