i pose it as a question, but i am already decided. imagine you have to write a modern game. dozens of programmers and dozens of artists. now imagine you have to do it alone? if you start top down, you can borrow an intro video. create an opening menu. go as far as you can, and then look at what you have to decide on classes and such. as a way to make a rough draft i think there is still a place for top down procedural programming. but then i also once posted "top down procedural programmers of the world unite" back in 2001 or so
cmon, cmon, put up your dukes! cowards! just kidding. i have never written anything with over about 10 classes so how would i know? it seems to me though that if it is so big you cant just see it in your head, or make UML then just start at the top.
save you $100,000 as well when you lay off the systems analyst