Build your layout with keyboard-layout-editor, paste the raw data into builder.swillkb.com, order plates from Lasergist or export files for a different service,

Build your layout with keyboard-layout-editor, paste the raw data into builder.swillkb.com, order plates from Lasergist or export files for a different service, buy switches of your choice (I recommend Kailh Box switches), hand wire them up to a Teensy or Pro Micro, set up QMK for your matrix and layout, and program it.