It can be done. Go carefully and slow. You should check out
Homegunsmith.com for more info. There are several people there that have built their own. Most are done with either full sized milling machines, or home smithy type machines. It is not easy, but can be done with a good drill press. You should also check out
The BUILDERS SQUAD Project to see what can be done with simple tools.
Advantages of building your own:
Pride in final product - being able to say ... "I built that."
No serial #
Extremely fun --- beats collecting stamps by a long shot
customize it exactly to your liking
Disadvantages :
Easy to screw up
It costs alot more than just buying a stripped lower
Hours of machining
You are not done with just machining.... you still have to anodize the lower
I would recommend buying a factory lower and assemble one. Once you have the bug, and want another one, then get a 80%er. Good luck, and don't forget to post pics of your builds if you decide to go that route.
A final note, if you think that you will be able to build one, and no one will know... wow are you naive, unless you have made all your purchases with cash and have no credit card ties for ammo or guns. If you have never bought a gun on a 4473, or have never made a post in a gun forum on the internet; you are going to be on some one's list somewhere. When the JBT's start shooting dogs in your neighborhood, they will be kicking down all doors, not just those that show up on the master confiscation list.
HTH
Mack