The harder part is learning to think in "high level" ways. The heroes have access to mass fly and have enough financial resources that they could get scrolls of just about any spell they might want to cast. "Your character dies" no longer means "roll up a new one," but instead means, "the cleric has to get over to you by the end of the next round in order to raise you without penalty." Fighting a roomful of brutes with a cleric and possibly an archer in the back isn't going to cut it any more; they need adversaries that are worthy of them, and adventure locales that are more exciting than a 30' x 50' room with some random clutter to make difficult terrain.
I do have some ideas, and a suitably epic long-term story arc, but it's the nitty-gritty of turning it into individual sessions that is the real challenge. I also have the entire 3.x-era run of Dungeon magazine and several Goodman Dungeon Crawl Classics to look to for inspiration, but those are only so much help. I tend to like my fantasy grounded in the realistic, even when there are elves and orcs and dragons, but when you reach this level, D&D's already troubled relationship with "naturalistic" fantasy starts to seriously fall apart. The system assumes, almost requires, that you start going all extraplanar, as the mortal world has just become too prosaic for such mighty heroes. At this point it's expected that you'll take flying ships to Asgard, or pop over to the City of Brass on the Elemental Plane of Fire to seek an audience with the King of the Efreeti. I, on the other hand, am still working in the mindset of coping with monsters rampaging the countryside. Granted, the monsters are giants now instead of hobgoblins, which does up the ante a bit, but it's still a quantum jump in scenario design that mentally I'm not quite prepared to make.