Definitely build your own.
I've done both; bought pre-built systems when I was younger, but I build them now.
- You CHOOSE exactly what goes into it.
- Can upgrade items easily down the road.
- Always cheaper.
- Can be a learning experience and quite a bit of fun.
- Will almost always beat a pre-built computer for the same price in performance.
- If a part fails, you have to contact the specific manufacturer for it. You cannot simply call "HP" and tell them the computer doesn't start.
- Always have to make sure parts are compatible.
- Can get tricky sometimes when building the computer itself.
In my opinion, the pros outweigh the cons. That's why I built my own, and with the help of this forum, I've been enjoying it very much.