Nine times out of ten I run published adventures. Always have. I rarely write up my own stuff, usually for one of two reasons. First, can’t think of a compelling premise. Or second, get lost in the long grass with overdeveloping it. Recently my weekly group hit a blank spot in the schedule so I had to pull together a game at short notice. I successfully fought the urge to go through my library, and instead got a blank sheet of paper out and started scribbling.
Classic opening; the PCs have been taken prisoner and are all suffering from amnesia. I liked the idea of an Mindflayer giving it the big monologue to the parties prone and semi conscious forms. That way they go tot see the villain before the final conflict with him. I said they had all been high level adventurers at one point, and this MF was their nemesis. Now he had captured them and essentially level drained them all the way back to 3. That gave me a campaign frame, and loads of design room for emergent memories and future plots that rely on a past.
The rest followed that basic idea. I made the dungeon an inverted ziggurat, and had it fly, though that part wouldn’t be revealed until later. I bullet pointed up a few rooms in the place (lab, kitchen, barracks, bridge, temple etc) and then dropped in a few events that would happened propel things forward. These were my fave bits. A delegation from the halfling settlement below, begging for mercy from the aerial threat. An ambassador from the Xarth Autocracy, a Beholder, come for dinner and nefarious planning. An assault by Pegasus riding paladins, devoured by a massive mutant cloaker. Clues to all these were scattered about, or visible as plot reveals in down time.
And it’s all gone swimmingly so far. I feel released from having to ‘get it right’. I can improv details and jot down notes as I go. I can react, steer or just hang on. And it’s fun to imagine things from nothing.
Should have done this years ago.
Treehouse: 
Awesome.