I have built from the ground up and from kits also many AR's. I have used Model 1 sales kits, Stag uppers, POF-USA piston uppers, and mil-spec parts builds. As long as the parts are in spec you will have a great rifle. The Stag M-4 upper w/rail and flip up sights is about $625 to 650. Model 1's start at $425 and go up from there (complete kit less striped receiver). Now the POF's they are $$$$ I ordered 8 of them ( I have a friend that was on there R&D team) for $825 with the rail, now they cost over $1000 and up from there. Make sure you get a chrome lined bore and chamber. Unless you are going to be in really crappy conditions don't waist the money on SS (it looks good). Go for the 2 stage triggers Model 1's are $80 (same as the RRA's trigger they don't make there own) they are easy to install and feel really nice. Be extra careful if you go to stone the stock mill spec trigger. Take it slow and don't go too deep or you will compromise the heat treat and how safe the rifle is. The flattops are cool but don't over look the A-2 full size rifle or A-3 flattop full size. You get the most out of the 5.56/223 with the longer barel. You can get the 6 position stock for it. That way you can make it shorter for CQB but still have the speed the longer barel gives the 5.56/223. Twist is up to what you shoot 1-8 is good for most of it, 1-9 is about across the range of what everyone is using, and 1-7 is mil-spec. There are a lot of little things you can do that don't cost a lot of $$$ to make the AR run better and shoot better, if you have any questions about them just ask. I hope you have fun building them.
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