Well as usual good advice from all. Thing with building your own is experience or skill level. Some guys can pick through the less expensive parts and fix things up and some get stumped, just one of the fun things of building your own.
I built a Commander on Caspain parts. It don't look pretty but it does run good. I started with less expensive parts that were "Milspec" and real cheap both price and quality. I got the gun running and then ended up replacing all the parts with better quaility parts from Browns, EGW, STI, and Wolf Springs.
You'll find when you price everything you need out you will be over the price of a brand new Mil Spec Springfield. Hell you may be able to buy a new Kimber for what you pay in quailty parts! Some say get a Milspec or a Kimber as a base gun and build from there. You have all your springs and pins and screws that you have to buy anyway. Just a thought.
Also don't over look the parts by Caspain, they sell most of what you need and they are very good parts. Also Gary Smith the owner has great customer service and advice too. I have not seen a Caspain catalog in a while but I think you can get everything but a barrel from them.
The thing I found out with quality parts is that the parts that are supposed to be straight or round or square or have holes those things are the way they should be, the holes are straight and where they are supposed to be. Not the case with some of the really cheap stuff. If you try and fit a thumb safety and it and the sear are lop sided you can end up wrecking those parts trying to ge them to fit. Good parts will be straight and less fitting will need to be done and you can concentrate on doing it the right way. Building is a test in patience anyway no sense making yourself crazy on top. Other than the fact that when you get it together and it runs you'll go crazy because you'll want to do another and another!
Guns are machines take a bunch of parts and throw them together and it takes a lot more work to figure out what is out of whack than if you know what your starting with.
Building your own is fun, and very rewarding and there is a great resource right here with plenty of people who will offer help. Like others have said here before me you get what you pay for. When you get a list up post it here and guys will make suggestions.
Good luck.
Ed