This article is buried in the ruins of Deskthority and needs new ownership and the kiss of life
Casemaking is an extraordinarily expensive mod, usually requiring either a sintering machine (for metal cases) or a very large 3D printer. There are quite a few custom cases that have been reproduced and mass-distributed by various manufacturers across the Tubes of the Internet. Usually, when you want to create a custom case, you'll have to have modeling software to create the CAD model of what you want to 3D print or sinter together. There is no possible way to describe the process for case-making, other than giving a general process description, which isn't exclusive to making keyboard cases.
1: Start doing research on interesting and comfortable keyboard designs (e.g. ErgoDox)
2: Start brainstorming ideas on what you want your case to look like, and what features you'd like to integrate into the design.
3: Find a PCB that has all of your ideal features, and adjust the design of the case to support that PCB.
4: 3D print or sinter that design into reality.
5: Assemble the case, with all of the components, switches, keycaps, and the like.
Feel free to post examples of cool designs and custom builds on this page!