Used the Simple Rack from Patrick Martin and designed it into a slightly reinforced / sturdier version.

2 print profiles / versions, one without extra cross bracing and one with it included. 

Highly recommended to add some wooden cross bracing across the entire back of the shelf for it to be properly sturdy and reliably hold some weight. Mine currently holds around 30 spools of filament like that without any problems.

Materials used:
Shelf Boards: 12mm OSB board, cut into 6 shelves, each measuring around 62x21cm (with added wooden cross bracing on the back)

Screws / Nuts: sized for M5 screws & nuts, each screw connecting the upper and lower bracket for sturdiness

OSB board I used: [https://www.obi.de/p/2572014/kronospan-osb-3-verlegeplatte-stumpf-125-cm-x-62-5-cm-x-1-2-cm](https://www.obi.de/p/2572014/kronospan-osb-3-verlegeplatte-stumpf-125-cm-x-62-5-cm-x-1-2-cm) 

If you try it out with maybe even bigger shelf sizes, feel free to share your experience!