Originally Posted by WoodenPlank
Depending on how much of your rifle you want to actually build yourself, you may need some extra tools. The castle nut on a carbine stock and the barrel nut on the upper both need to be installed and torqued correctly, or problems can result. To do that requires an AR-15 armorer wrench, a proper bench and vice, a torque wrench, and receiver blocks. If you don't already have most of those items, that can result in a significant investment.
I concur. Assuming you can get all the parts, buy a stripped lower and install a stock and lower parts kit. Then buy a complete upper and bolt carrier group.