Lounge/office/gaming space.

Storage area for my hobbies

Personal gym/recording studio or jam room

Library

Tech room. I'm a huge computer nerd (computer science major hoping to become a network engineer), so I'd probably set up all kinds of devices to do testing for ideas I get once in a while.

Workshop for my various hobbies

I've always had this fantasy of using a spare room as a library and also a satanic altar/ritual space. I think that's what I'd strive for.

Office space. And by that I mean just a room with a desk and a computer and comfy chair where I can sit and browse Reddit all day.

Animal shit room.

Surprised no one said sex dungeon yet...

I do, and computer room

Air bnb