Yep Barry is right; first choose what CPU (AMD\INTEL…then what one can you afford) you want then that dictates what motherboard you can have. I went with AMD and the Asus motherboard I got had built in sound so that was cool.
With the money saved splash out on a top gfx card or more RAM (also dictated by motherboard you bought but it will more than likely just be whatever the latest RAM there is out there)
So the way to go about it is….
By building your own you also dont have to pay for mandatory windows (they still do that yeah?) that manufactures charge you.
Stuff like motherboards tell you what type of CPU they can take [dictated by the socket(s)]