See, I wouldn't have a problem with the desire for a private room at ALL if it wasn't pretty obvious that weed was the only real reason for needing this room. When you get older, you need privacy, sharing a room with your younger sisters isn't good for any involved, but if you just want your own room to sneak around and do things your parents don't want you to, then you need to serious reevaluate your place in the family. You should have a say in what happens in your life, you should be allowed to voice your opinion and have it matter, but you should not go against your parents' wishes by smoking weed in their house. That shit could get them in trouble, depending on the laws where you live. It's a shitty world and pot is illegal, and getting busted can seriously fuck up your life. It's not fair, but the world is faaaar from a fair place. So go for the new room, try to get them on your side, but when you get the urge to smoke, roll a j and take a walk. You don't have to quit smoking, you just don't need to do it at home.