I've been doing that myself recently. I have a 3d printer, so I took the dxf plate generated by builder.swillkb.com and just extruded it in OpenSCAD a bit for s

I've been doing that myself recently. I have a 3d printer, so I took the dxf plate generated by builder.swillkb.com and just extruded it in OpenSCAD a bit for some thickness. 3D printed it, put it together with some screws (the generator even comes with screw hole options), hand wired the switches together, to a Arduino Pro Micro and programmed it with QMK.