Gaij, mate, you don't need to go to an armorer, all you need are three different sized roll pin punches and other common household tools and you can go to town.
I built my STAG with a DPMS inners kit and I used a Philips head screw driver instead of Roll Pin Punches, tha when I found out the hard way that won't work. I purchased new roll pins and the punches and went to town.
Brownells is the wource for the punches.
Check out the link homie, everything you should need(information wise) is there......
AR15.Com Build Yourself