First, no, you're not unusual to need your own personal space. That's perfectly reasonable.
I don't see why it's such a problem though... Presumably "their" room is the Master bedroom of the house. Why not switch the beds around, making the Master bedroom back into The Room? That leaves the smaller room to be your personal room. Let them know that your work habits and personality require you to have your own private space. Have them agree not to come in there without your permission, and never to leave anything behind. If they don't follow that, put a basket outside your door where you can chuck their crap when they leave it there. Empty the basket into their closet when it gets full. They'll probably get the hint eventually.
Gralson: my husband (works out of town).
Auto: my girlfriend (lives with her husband Zoffee).
The most dangerous phrase in the English language is "we've always done it this way."
Last edited by SchrodingersCat; 11-18-2012 at 07:19 AM.