This is T. Foster's. I think I read about it at Knights and Knaves Alehouse forum.
Don't think of this as a set-in-stone flowchart. Think of this as boundaries to help you when you're floundering around early on in dungeon-making or when you're under the gun to produce something quickly.
The idea is to have at least this much ready for one night's adventure gaming. Twelve rooms holding:
One Session of Play
1 Major Encounter
2 Major Encounter that Overmatches the party
3 minor encounter
4 minor encounter
5 Telegraphed Trap
6 Trick/Puzzle with a Permanent Effect
7 empty room
12 empty room, with some kind of False Climax
I think it is pretty self explanatory. The false climax and permanent effects are very old school flavor. As is the dangerous encounter that is really too tough for the party unless they out think it (or run like hell). Telegraphed trap means a trap that is obvious about its presence but maybe not its function. The idea is that traps are actually more dramatic and tension building when players know they are there. I picked this idea up over at Ars Ludi.
What I've found myself doing is thinking in chunks of two of these and allowing for player to go in two entirely different directions. Hope this is helpful.