I've never made a roguelike before, and it has probably been 15 years since I have played NetHack or ADOM. But...I'm going to try and make a turn-based cave-flyer sort of game using ASCII on a hex grid.
The plan is that you will start in the center of a tunnel-riddled asteroid, with the ability to walk around on the walls and jump across open spaces (zero-gravity environment). Then you can find various items and weld them together to make ships to fly around, with the goal being to collect treasure and find an interstellar drive so you can build a starship and warp back to civilization.
We'll see how it goes...