Go to Numrich Gun Parts and browse around.
The main parts groups that you will need are:
a barreled receiver group, stock, operating rod, operating rod spring guide, operating rod spring, gas cylinder, gas cylinder piston, trigger group, magazines, sights, and bolt.
I can't really give you an exact parts list, because it depends on how you buy the stuff. Some sellers will sell a "group" of parts together, and some will sell them separately.
For a complete barreled action, try
here for forged. Expensive huh?
I don't know what your exact goal is from your post, but if your reason for building vs. buying is to get an M1A/M14 on the cheap, you'd be best off by looking for a Chinese Polytech or Norinco that has made it into the states before the ban on Chinese guns went into effect. They will generally cost around $600-$800 if you can get a good deal on one. Springfield is the next cheapest option, with a standard model going for about $1300, and a Loaded model for about $1400-$1500. Springfield has cast receivers, the Poly's will be forged. Some folks think it makes a huge difference, but a cast receiver done right will outlast you. Forged is the way the USGI receivers were made, and so that's what many folks prefer, but it will cost you a pretty penny. IMHO that is money that could be spent on things that will have more of an affect accuracy, or on ammo.
I will suggest that if you want to shop for parts, go to the "PX"
here. Their site is a great source of info, and everyone there is extremely friendly and helpful. They will be more than happy to assist you further if you choose to build. You might even find someone who wants to sell a lightly used M14 for a good price.
Best,
Jason