The folks at trenches have an interview with Cedric "Inoxx" Fiorentino, the chap behind the INOXX map pack for Unreal Tournament. Its an interesting look into the mind of a top map designer. What he does, and indeed how he does it
"For UT you don't have a story or a progression in the game. So you're completely free to do anything you want. For Unreal that was different, we had to make sure the easy levels where at the beginning, coordinate things with the other level designers..."