building is quite easy. people often compare it to building LEGO = you just read what goes where, and plug it in. most of the cables are made differently so its hard to put stuff in wrong slots. its alot more intimidating than it should be, i had the same thoughts as your the first time. recommended!
but if you're dead set on a prebuilt = it would probably be a good idea to tell us your budget
and what settings you wanna party on (high/low) etc. i'm not sure, but i think most horseshit computers for around 500-600 dollars can run skyrim on low settings and dota2.
http://www.newegg.com/Product/Product.aspx?Item=N82E16883227443did 1 min search, u can find better if you do some research, but something like this is what you're looking for probably. im no expert, and i don't intend to do the research for you, but i'd estimate that this can run dota2 fine and skyrim on medium settings. i'd go for something better(and more expensive) tho!
you'll probably get much better help if you post on computer forums aswell.