I built my first AR15, still have it. Dang proud of it. But since then, I changed my mind and desires on what I want on my next rifle and so I have bought only Factory rifles, Armalites. I agree, if there is a chance for you to resell, most folks would want a factory rifle as in a factory matched upper and lower. Changing out the buttstock and other assessories, does not seem to hurt the basic price. And so it is easier to buy and sell a factory rifle, then a custom made rifle. The term Frankengun seems a bit exteme for the AR platform, but it does make the asking price drop more for an unmatched upper and lower. that is what I have noticed online and in the gun shows. Either way, its a learning experience!