How do I get my parents to build me a room?

I'm a 15 year old girl, and need my own room. We have a 3 bedroom house, and my parents sleep in separate rooms, because my dad snores. My dad has one room, my 17 year old sister has one room, and me- my mom- and my 6 year old sister share 1 room. I need my own room, teenagers need their privacy. I've been stuck in that room for 2 years. I need help! My parents don't have a lot of money, but I dont wanna have to deal with all the toys, stuffed animals, etc. For any longer. Help!!!