If you are thinking Ar 15 think ar15.com That's where you can find most of the makers on there indstury page and you can find some good deals on parts in threre equeptment exchange. Some good places to get lowers and uppers are armalite,bushmaster,RRA and dpms as long as you buy a forged upper and lower with a good barrel you will be ok .I have heard some bad post about ASA modle 1 and M&A mainly costomer service but I have never heard any bad stuff about RRA.
I was doing the same thing you are about 9months ago I was tired of the inauccary of my mini and the lack of good aftermarket parts so I thought "I'll build a AR15 "What I found in my case was by the time I buy a lower +parts kit +good trigger+ butt stock = plus 4 diffrent shipping charges 99+50+90+50 +5+5+5+5=320 That does'nt include the tool you will need .Or I can buy a RRA national match complete lower put together by the factory with the factory warranty for 300 shipped.I found the same thing with the upper .A stripped upper+barrell+hand guard +bolt carrier group=100+200+50+100=450 or I can buy a complete upper from RRA for 480 thats 30 bucks more for a factory assembled fully warrantied ready to go upper.And agian I did'nt include the tools you would need to build your own upper.
I was doing the same thing you are about 9months ago I was tired of the inauccary of my mini and the lack of good aftermarket parts so I thought "I'll build a AR15 "What I found in my case was by the time I buy a lower +parts kit +good trigger+ butt stock = plus 4 diffrent shipping charges 99+50+90+50 +5+5+5+5=320 That does'nt include the tool you will need .Or I can buy a RRA national match complete lower put together by the factory with the factory warranty for 300 shipped.I found the same thing with the upper .A stripped upper+barrell+hand guard +bolt carrier group=100+200+50+100=450 or I can buy a complete upper from RRA for 480 thats 30 bucks more for a factory assembled fully warrantied ready to go upper.And agian I did'nt include the tools you would need to build your own upper.