How do I get the biggest room in my house?

Basically there is an amazing room at the top of my house and I really want it. Its a house of 5 boys and 2 aren't bothered really which room they get but I sense the other two (and obviously me) want the top room. I can't stress how much I need this room. I've heard all the bull**** ways of picking rooms i.e. pulling straws etc etc. I need a strategy, some sort of economic algorithm that can assure me the top room. How can I manipulate their mind's into giving me the top room? Surely there is some sort of game theory or something that can allow me a better advantage - surely? If it got to the stage where we had to debate for the room could I pull out the girlfriend card? I mean it basically means I am going to have a second person in there more often than not hence why I need the extra space.

Please someone help - I need this room.