I just added up the parts for the first time. The price ended up within $25 (including shipping) of a BCM complete upper with hammer forged barrel (after the BCG and CH is added to the BCM).
Unless a person wanted to build it for the experience (or wants a non 5.56 barrel), building a higher end upper really won't save any money. Finding the exact barrel length, hand guard, gas system length, etc in stock may take a little searching/waiting but it's possible to find it.
There are a lot of people that believe that all lowers that are within spec are pretty much equal, and I'm one of them. If I had a Stag lower, I'd have no problem putting a top shelf upper on it. I've read that a lot of builders use Stag LPKs, so the small parts should be GTG. As long as the buffer tube is mil spec, it'll accept any of the better buttstocks. Naturally, it'll also accept my favorite stock, the UBR.
There are also those that believe it doesn't make sense to build a high end rifle with mid grade receivers, but a lot of that may stem from people that are overly "brand" conscience.
After I've put my final 1,000 - 1250 loaded rounds through my 223, I'll have no issue with screwing a new BCM, White Oak, Noveske, etc barrel into it, replacing the BCG with a full auto BCM or LMT unit, adding a FF quad rail, and running my lowly 13 year old DPMS for another 5-10K rounds.
