If you're wanting to build your own miners for BTC, you're either gonna have to go to an existing manufacturer like Bitfury with at least $1M for an order of their ASICs, or come to an existing IC developer with about $10M (and around six months) to run you out your own custom design. Unfortunately the only "realistic" course - unless you have a whole lot of money you're willing to risk losing entirely - is to buy existing miners from someone else.