Quoted: how much cheaper is it to build an ar than to buy one for the same rifle. I want to spend around 600 and havent seen any complete guns around that price, so i think ill have to build it.

To be honest, it all depends on what you are looking for.  If you don't mind a few used parts, you should be able to come up with something in that pric erange without much trouble.  A used upper is often pretty cheap, but make sure you know what you are  getting.  A 14.5" barrel isn't legal, but a 14.5 w/FS perm attached is legal because it brings it out to 16".  

Do a lot of looking before you buy, and you will get a better idea of what you want, and how much it should cost you.  AR15s are modular weapons, so you can buy parts a little at a time if money is tight.  

There are plenty of people who buy a stripped lower first for roughly $100, the lower parts kit (LPK) for another $50-70, and then a stock for another $50-75.  That gets them all new parts on the bottom half.  Then they check the EE boards and gun shows,  and wait until they see a price and upper they like.  Just make sure that when you look at uppers that you check and see if the bolt carrier group comes with it.  If not, a new one is roughly $100.