Pro;s and cons about building your own. First up, tho, is the myth that a built gun to milspec is somehow better than garage built. That is not a given or guaranteed - milspec guns in service show that the extractor and bolt get replaced at 25,000 rounds, action springs after that, the barrel should be replaced due to gas erosion at the port near 100,000, and extensive full auto use will ruin the throat and accuracy very shortly making it an 8MOA gun when the armorer finally sends it to Depot for rebarreling.
That's a Colt or FN. Don't let the fanboys tell you different, guns in service are not indestructible.
Can you build one cheaper, no. Makers who buy parts in volume are getting the best volume discounts, retailers who sell you 1 lower, 1 upper etc at a time are marking it up. Volume buying lowers puts them in them under $25 each. We don't get those prices. Same for barrels - if you can get them for $45 each milspec we'd be busting even. Not happening when you buy retail. The fantasy you can build cheaper is exactly that -
Another issue is controlling dimensions on parts that must match to meet customer expectations, like the pin locations on lowers and uppers. We like them to go together with thumb pressure and no rattles, that is what the makers finesse selecting their machining tolerances and during assembly. Can we do that? Nope, not happening. We get a lower from one coast, and upper from the other side of the country, finish assembling and try to pin them together and we get what we get. My first build was so tight I literally used a small deadblow hammer to "assist" the pins and get them to fit. Now? Almost thumb pressure looser, things are breaking in. The second build I dropped the upper on the lower and it not only fit it was a tad loose. Like, a rifle that had seen a few cycles in Basic.
Your Mileage May Vary - no telling what you get assembling your own, but even the cheaper guns built off the rack do that pretty well.
As for what kind of AR - they just don't make them all. First gun I built was a A2 stocked 6.8 dissipator. Those are nearly impossible to find on the shelf. But, since I had put it together, I could change it. It went to a MFT Minimalist adjustable carbine stock with Apex Gator tube. And the leftover parts - the clamp on FSB - became a 10.5" pistol build with B5 handguard. Can't find that on the open market, either, much less OD green Magpul K grip, and cut down carry handle rear sight.
You build because the makers always play to the market and make the popular model. They don't make the niche guns or any retro models. You can't get an M16 a nothing. You build it.
As for tools, don't believe it for a second. The first build was assembled with vice grips, the barrel nut tightened with a large pair of channel lock pliers. "$200" worth of tools is not a requirement and the build it yourself sticky on the AR forum shows you exactly how. The builders ten years ago didn't have any special tools and didn't really need them. I now have two specialty tools for the AR and I've used them less than half a dozen times, one was a waste of money for the most part - a nose lapper - the other is the barrel nut wrench which is also nearly useless. One quick way to know the poster hasn't got a true grasp of the mechanics is when they start on using a torque wrench, which is entirely unnecessary. If you are experienced about threaded fasteners, you know you can go too far, all the torque wrench does is keep you from doing it. You do NOT use it to torque a nut to a specific tightness, it's an indicator that prevents you going too far. It's doing the exact opposite of what most think it does. It's just there to stop you from stripping the threads - it's not a lug nut application and the barrel won't fall off.
As for pricing you get what you pay for, however, when you specify a particular roll mark you are also buying provenance. If you want Colt over S&W expect higher resale and some slight differences in fit and finish. Chain them both to the bumper of your truck and drag them down a dirt road and that goes away. Then it's a matter of reliability, and for the most part even if a full milspec gun, you are right back to changing out the extractor and bolt somewhere around 25,000 rounds, the action spring sometime after, and then the barrel depending on how quickly you abuse it with mag dumps. That is going to happen regardless and no rollmark can prevent it.
Buy if you want, build if you need. Best way I can put it.
