Quick question... can you please fill in the blanks? What do you intend to do with the rifle? Give us as much detail as you can. I'd spend hours reading about ARs right now, it's by far the best favor you can do for yourself. We'll be glad to help but give this a lot of thought.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek