How to design and build your own module? (documentation and schematics)

following a previous post, I was interested in developing my own module ( a linear CCD, hence not a simple shield). I could not find any PCB design of the OpenMV on GitHub or in Hackaday. I could not find also some documentation regarding the communication between the camera module and the mainboard. Where I can start? Is there any tutorial and any schematics at least for designing an add-on module?
Thanks for the help!

All the design files are hosted on github:

But we don’t have any documentation for designing modules.

Okay, thanks a lot!