If you feel comfortable doing it and think you follow instructions, do it. If not, get pre-built. These forums are filled with hundreds of posts a day of people "trying" to build their own that break pins on the chip or motherboard, snap the fan brackets, can even figure out how to boot from a DVD to install windows, put cards in the wrong slot, don't understand power and power rails and the best plugs to use to power, what etc.
Then there is the 100 threads a day of "this is my first build and I get no power or no video or it beeps at me".
It's not hard, but if you're not comfortable doing it, don't. Everyone who says it better can do it blindfolded and it's not a big deal to them. I just put together two A8 AMD system from parts in box to ready for OS in under 30 minutes for both, but does that mean everyone can and won't force the RAM in backwards and bend pins, no.
I know an oil change is an easy thing to do but for that, I go to my mechanic. I rather not mess around with my car, not my thing.
Moral of the story is, what is easy for one person, can leave another person with a fried PC that they never even got to boot up once.