My parents won't let me get my own room?

I'm 15, and its unfair because theres an extra room where no one sleeps in there. Everytime I ask them why they make an excuse of saying "If you get your own room extra electricity and heat will be used and it'll cost more." WTF? My little sister hangs out in their room most of the day. I've been sharing a room with her for my whole life! It's not just that, I can't keep my laptop in this stupid *** shared room at night. I can't go outside. I stay inside like a no lifer. I can't wear shorts, even to the beach or when its like 100 degrees out! My parents also make me feel bad about myself and make my self esteem go down. Calling me ugly and etc. UGH, what can I do?! I hate my parents and this house and my life.