Summary

https://github.com/TheBrainlessEngineer/Marble-Safe/

or

https://youtu.be/sPzw5k4Us0A

for more info, and assembly process.

Parts needed (other than 3D-printed)

M3.5 x 16mm Screws x4
6.35 mm x 10.3 mm springs x4
608 2RS Wheel Bearing (8x22x7 mm) x4
(or more if you first have to get the fit right)

Parts that i used (no affiliate links, i dont get any money if you buy these or others)

https://www.amazon.de/gp/product/B088NY4MG6
https://www.amazon.de/gp/product/B08R65BKFT
https://www.amazon.de/gp/product/B07N7QGXNZ (the parts are included in sets, so it would be waaaay smarter to buy them seperate i guess)