Most kids share rooms, because there aren't enough rooms in the home. Assuming this is the case, there is not much you can do with your parents. If it's not the case, ask your parents what it would take to turn the basement or attic into a room for you. They will resist, but keep on it. You can tell them that you will keep it VERY clean, you will help clean it out. You will submit to weekly "white glove" (means very clean) inspections - just what will it take?

Since I'm betting it is the case, you have only yourself and your sister to work with. Save your money and buy a locking box and a combination lock. Then buy some candy (if may work easier to buy some she likes and you don't). Teach your sister to clean her side and reward her with candy (obviously - you'll need to keep candy on hand but locked in the box). The box is also where you will keep your personal items, as eventually she will have access to high shelves and be in your stuff. That WILL happen, I'm sorry. (I was the little brother.)

Believe it or not, if you try to make friends/piece with your sister - it will help you in college - where roommates might steal from you, leave messes, never do dishes and the like. Figure out what you want from your sister and teach her how to do it. It is the best thing you can do at this point. Best of luck to you.

Put her bed in the closet.

I am 13 years old and my sis just turned four and I've been having to share a room with her? She is always making messes, throwing fits, and she has tons of little kid toys and she has doc mcstuffins blankets on her bed. Im always so embarrased when my friends come over because none of them have to share a room and their rooms look cute while mine looks like two toddlers share it. I can't even go in my room at night until I'm ready to go bed because she's sleeping. My parents won't do anything about it. And everytime I think of how we have to share a room I get so mad and want to cry. How can I deal with this?