Mine is currently my closet. There's even a portal to Knarnia, but that's an insiders' joke. Soon (read: in a few years) it'll be my whole apartment, but there are a lot of things that need to happen before that can happen. And it's not called TARDIS, it's called SIDRAT. Which stands for something, but the notebook in which I wrote it down is currently at my parents' house and I am not. So I can't remember what it is.
My TARDIS has no form, I just close my eyes and think of my TARDIS and open my eyes again Im there....never have to remember where i parked it. And if i pick someone up i just hold their hand and they go with me :D