I can expand a bit on Hineline's excellent post. It is very important that you finalize your design before you build as you can not make replacement parts or replace parts for any reason. There is one exception to the "no replacement" rule. The ATF allows you to replace wipes after cutting up or burning the originals. While wipes suppress very well for pistols, they last only a few rounds, so they are not worth messing with on a rifle.
Check out http://www.subguns.com
for forms and advice, and http://www.silencertests.com
for advice and drawings. I feel that it does not take an expert to make a good silencer. I bought a 12x36 grizzle lathe, grinder, welder and hand held band saw solely for making silencers. About a $2000 investment for 7 silencers so far. It does not take much time to learn how to make parts to within one thousandth of an inch for silencer parts on a lathe. Learning to weld is harder, it definitely is an art.
You can use all aluminum for pistol and lower pressure (22lr, 22 hornet, whisper cartridges) rifle cartridges, but it is a good idea to use stainless steel for the first (blast) baffle as it is subject to much erosion from the un-burnt gun powder particles. You are asking for trouble if you use aluminum in any silencer intended for use on a 223 or 308 and higher. The softer stainless steels such as 304 are just fine unless you intend to use them on a machine gun. There is information available on the net for anodizing your silencers. I just paint mine; if they get so hot they blister the paint, I can just sand and re-paint. I use a small hand engraver instead of bringing the tube to a someone else. It looks rough, but then I only care how well they sound and last.
If you decide to sell your silencer, you will probably not get much for it compared to those made by nationally known manufacturers. It can be transferred to a person in your state using a form 4 and the $200 tax, or to a person in another state through a dealer with two $200 taxes. It can go to your heirs after your death tax free on a form 5.