As for build a primitive one at home, (assuming one == machine controlled knitting machine) see the journey of Gerard Rubio from OpenKnit to Kniterate

https://www.labonthecheap.com/the-openknit-machine/ https://www.kniterate.com

If out are willing to move the carriage back and forth manually, and transfer yarn manually (for increases and decreases, etc.), the route to go is buy an electronic Brother machine and replace the electronics. The old standard was the AYAB board that you constructed yourself. (the evilmadscientist.com version is no longer in production) https://www.ravelry.com/groups/ayab for help and to meet fellow travelers. (circuit board and components: https://www.etsy.com/shop/redpinkgreen)

The less DIY more professional looking way is the recently released eKnitter, which replaces the electronics, but in a manner that more closely resembles the original form factor of the machine. https://eknitter.com/produkt/eknitter/

Okay, one last project to share. If you are more a start from zero sort of person, see this wonderful set of videos on designing a 3d printable manual knitting machine. Realistically, more of a wonderful educational process you should see, than an economically viable one. (Meaning you can buy used mass produced hardware for cheaper.)

https://www.youtube.com/watch?v=kUKiXIdw2pI&list=PLWDnfcUpk7...