If I were you, I'd go with a refurbished Dell. We have three in the family at this point, and they've been good systems that didn't cost all that much.
Mine is the oldest - a laptop that's approaching four. Haven't really had any trouble with it that wasn't my own fault in the end. It IS starting to have parts wear out, as I've mentioned...but considering how hard I've been on it, I can't complain.
I wouldn't wanna build a system myself. The benefit is that you know what goes into it, and if you LIKE that sort of thing (I don't), it can be a fun project. Also, if you catch the right sales, you can potentially save a bit of money, though not as much as was once true.
Downside is that you have to contact the manufacturer of different components if you have a failure, and know enough to KNOW which component has failed in order to do that. No one stop shopping for service. And you obviously won't have a warranty on the full system.
Ruh Roh Raggy!