Unless you have expert machining skills and really think you can build a top notch product, your item will have to go through a local in state NFA dealer. So your best advice the first time is to contact them and buy something and let the profesional walk you through the process. He will know if the CLEO allows it in your area or not, etc.
Since your profile shows nothing we don't even know if silencer are legal where you live so it's pretty hard to give advice.
Once you have done it once, then it will be easier to do something on your own without help next time.