Is your goal to save money vs. buying a complete gun? Because as the market stands now, you can't do it. Less expensive to buy a complete gun than to try to pick up all the parts [& there are many req'd!] and assemble them on your own.
If your goal is to have the experience & maybe put together a higher quality barrel, trigger group, etc. into the rifle, well, then maybe it is worthwhile.
Just remember that there are 2 competing non-standard standards out there: the AR-10 [based upon the nouveau Armalite trademarked product] and the 308AR [based upon the DPMS & other competitors' "AR15A2 all growed up" build parameters.] The two versions aren't compatible with each other, and not all parts are even compatible between other competitors' versions of the same type.
Yeah, building your own can become quite a headache. If you're determined to go down that path tho', you'll want to build a 308AR: there's more pieces parts on offer for them out there, so the costs are lower.