I'm in the process myself.
I have specific things on my list and thought a ground up build from a stripped lower was a good idea.
Step one: I couldn't find a stripped lower! lol
Got a complete Stag lower instead, then found a stripped Spikes Upper.
Now I can't find a BCG, Barrel, Gas System, or HandRail in stock anywhere. Let alone the stock/grip that I want.
So, I pre-ordered a complete upper today instead.
Who knows when it'll be in stock, but at least I can stop searching the depths of the internet for unobtainable parts and just keep my eyes peeled for a stock, grip, buis, rds, free-float rail and muzzle device.
If you can find a quality rifle in the length that you want, buy it and swap out what you want as it becomes available.
Edit: Buy any mags you can find!
Questar has loads of lar mags and NOBODY has any pmags.