I want a carbon (maybe steel??) cross bike with disk breaks (to be used for all around, get down and dirty, commute in the rain/slush/etc... going on muddy/rough trails).

Should I try to find one pre-made or would it be worth buying the separate components and putting them all together? Would building save me money? Some of the bikes I am looking at are far beyond my price range and they don't have the disk breaks so I'd have to spend even more money on those!