Before answering your query, I will ask why you want to make your own mixer. If you are a developer, then you will not be asking this question in the first place, but let's say you want to get started or want to get an idea of how mixers work. That's why you are asking how to build them.

Secondly, I will say making your own mixer is not an easy task. I am not talking about the coding or funds (yeah, you do need a lot of funds, like BTC if you are planning to make BTC mixers only and other alts if you are planning to make alt mixers).

I am talking about legal cases and pressure from the authorities, and you should have a good knowledge of how to deal with bad usage of your product in action, which means you should have competitive knowledge and skills to deal with live problems. Overall, I will not provide any answers or links, as many other members have already done that. But I will suggest you play it safe.