I needed a small, but decently powerful computer that had at least 2 display outputs so I could present my art live at cons.
A lack of support for Corel Painter on macs combined with a general growing frustration with them (NEVER had a problem with my gaming PC) I decided to build a mini-itx computer.
Cost me around 800 bucks, windows licence included. Nice little case with decent power, liquid cooling, 8 gigs of ram and a solid state drive. No video card since Painter just uses the processor and I'm not playin' games.
I had a friend help me put it together. Wasn't too hard. A lot like working with lego. Without help, it would have taken me twice as long, but with the amount of 'how to' videos about building your own PC I could have easily done it myself. If it were in a standard sized case it would have been easy.
This site lets you pick parts and lets you know if they will work together (saved me a TON of headaches) PC part picker
And reddit has a community around first time PC builders.
Ended up looking like this:
Snugs right inside my easel.
And if something eventually breaks/wears out I've got the know-how to fix the problem myself, now.
Good luck if you decide to build your own! I found it a rewarding experience.