I-is-Zed

Newbie to modding here, and I'm looking to make a very particular mod. I want to have the option when creating a new world to generate a void world, except in that void world, I still want structures and villages to spawn floating in the air. Now, I have absolutely no idea how to do this, so what I need is pointers to what documentation I need to read and what things I need to learn in order to make this real. Any pointers in the right direction or tips are appreciated.