If you can build yourself, prebuilt is always a rip-off. Paying for parts you don't need, replacing those parts etc. It's not that hard to build a computer. If you know how to use a screwdriver and read. Motherboard manual tells you exactly how to do it. I built my first one in 2000. There was no youtube, nothing, just the mobo manual to go on. Came out just fine. Watercooled too, when there were no kits to buy, none.
CPU decides what motherboard you need (socket). Also what memory you need, DDR3 or 4.
The rest generally works on anything, as long as motherboard has the connections. Most of the stuff is standard but m.2 is new and not available on every mobo. USB 3.1 is another that might not be standard yet. Can't think of anything...