Before building (or buying) your computer, think long and hard about the software you’re going to want to run and what you want to plug into the machine.
It’s got to be said, that not only is Logic MUCH cheaper than its competitors these days, its more and more widely used on a daily basis. Pro Tools has kinda fallen out of favour a bit, Cubase has almost gone by the wayside, and none of the others really have the all encompassing power of the big three, even if things like Ableton live are pretty good for specific types of music.
With that in mind, I’d really think long and hard about going down the mac route, or building a very good Hackintosh to run Logic. For advice on either, I can help as I’ve quite a bit of experience of both.