Zac - Well you are in the right place, go check out some of the threads "stickied" at the top of this section. Then be prepared for more information than you want.
Seriously, the first thing you need to decide is "What do I want this AR rifle for, and what do I want it to do?" There are SO many choices and SO many options. Take a bit of time to decide what end-product you want, and then post back. You will be flooded with advice (and preferences!).