I have thought about building an AR but I feel that it would cost more than I could pick one up for. I would keep buying really nice everything and the price would double easily. I do have a buddy that says he would help me though.
Jeremy
Depends on what you're looking for. If you're planning on installing a nice trigger, or aftermarket BCG, or stock beyond the basic magpul stuff, etc, you're going to spend comparable amounts doing your own build, maybe even save money, if you're smart about buying. If you don't really care, and you just want a relatively stock AR, yeah, you can get one for anywhere from under 500, to around 850 for a Colt, based on what I've seen lately. If you want a fancier receiver, you're probably going to want to build. If you want a premium barrel because you're trying to build a tack-driver, you want to build. If you just want a battle rifle, and you aren't picky about what parts you need on it, you're better off buying, particularly if you don't have the tooling. The other nice thing about builds, however, is that you can buy parts here and there, and so each individual expenditure doesn't feel as bad. You have to be careful about eating shipping costs, as that can drive up the cost of the build significantly, but it can make a build go from the "not gonna happen for another year" category to the "just finished my build" category.
As far as piston guns (like the Ruger) go, anything with a piston is, IMO, dangerous from a maintenance perspective, because the designs aren't standardized, and, unlike a DI gun, you can't just get new parts easily from anywhere. You have to get it from the manufacturer, and hope that they're still making them. I personally won't own any piston AR's until/unless pistons become mil-spec, or standardized to the point at which the EXACT design is supported by multiple manufacturers. YMMV.