Yep, I do all my own designs. When I got into the hobby in 2014, there weren't nearly as many ergo designs floating around (at least that I was aware of!), so I learned OpenSCAD to design a keyplate and 3d printed it, with a big awkward block of foam for support. I used that janky keyboard as my daily driver at work for at least 4 years. If your keyboard is perfect for you, it doesn't have to look perfect!
I mostly built the 120% because it was quite a challenge to play Final Fantasy XIV on a compact split ergo. (And because my girlfriend gifted me a set of Evangelion keycaps and it felt like a huge shame not to use all 127 of them.) It was pretty much an excuse to fit all of the keycaps that I had into a mostly normal keyboard layout. The extra keys are things like F13-F24 (poor OS support on those but I remap them to useful shortcuts for FFXIV with AutoHotkey), media controls, a language switcher, stuff like that.
If you want to try your hand at creating your own designs, it's actually not that hard to get started in my opinion, at least from a hardware perspective. I went from never having soldered or 3d printed before to typing on a working keyboard in the space of a weekend hackathon. All you need is the electronics hardware (microcontroller, keyswitches, keycaps, diodes, wire) and some form of keyplate and support. I would recommend lasercut acrylic since it's not very hard to get started with the 2d design with a variety of software options. If you have 3D printing experience and access to a printer then that might be quicker and more convenient.
I have a few designs on GitHub if you want to take a look:
The Sandiego [1] was my first design and so the firmware is pretty simple, so it might be an okay starting point there. I used OpenSCAD for the keyplate design and didn't make a case ever. There were wires hanging everywhere and it was a guaranteed conversation starter at work. Entirely handwired, so no PCB design either.
The Sigmar [2] has a keyplate and case designed in SolveSpace, which worked ok but it was a bit tedious. For this sort of 2D design, I think it was overkill. I used QMK for the firmware, which was kind of a pain in the ass to be honest. I probably wouldn't use it again. You get a lot of features built in for free though, which is definitely a selling point. I did a PCB design in KiCAD and I would absolutely recommend doing the same for your second keyboard. (Wire one by hand first!)
The Type K [3] is the 120%. Did the keyplate and case design in straight Python, generating DXF files for lasercutting. (I made a few mistakes in the design which I had to bodge with a bit of drilling...) The firmware is a beast because it has no dependencies on any USB libraries or anything. Wouldn't recommend that route unless you were seriously interested in USB, but it was definitely educational. PCB design again in KiCAD.
[1] https://github.com/smrq/sandiego/tree/v1
[2] https://github.com/smrq/sigmar-keyboard
[3] https://github.com/smrq/type-k-interface-02