You forgot to include the OS...
Just messing with you.
I don't understand why we are arguing about this. It is never a bad idea to build a PC if you or someone you know knows what they are doing. Most people though can do just fine with a pre-built. When you are doing more intense stuff like gaming or 3D rendering that require better RAM and video capabilities, it becomes almost necessary to build your own. Either way, it all comes down to budget and personal preference.