You want to build something completely from scratch? Making cups, baffles, headbands, earpads, etc. I assume you're going to source the drivers from somewhere rather than build your own?
You're not going to find many basement nerds who have the capability or equipment to machine/manufacture large quantities of headphones. I have plenty of DIY experience and transplanting drivers (see signature for links), and a good ear for tuning, but I don't know if that's what you're looking for.