How can I get my 'parents to give me more space?

My closet is full of all of their crap, underneath my bed (I have a bed where you life it up) is so full of their crap it just closes, and the same goes for my drawers.

I do have some drawers and some closet space, but the vast majority is taken over by them.

I have tried telling them about how all of my friends have bedrooms to themselves (except if they share with the siblings, which is different) and can do what they want (to an extent, obviously). What else can I do? They think because it's their house they are entitled to the space, which I do understand, but I am a young adult (20, nearly 21, so nearly an adult) who needs personal space. All of my stuff is scattered everywhere and they are always moaning at me for being untidy, but they don't understand that if I had more space to store things it would be tidy.

It's unfair and they can't understand the problem. They think my friends' parents are pathetic because they let my friends 'walk all over them', which is just stupid.

Another thing, they are seriously controlling. They have read my journals before and shouted at me for what I wrote in them, when it is personal, they won't let me have driving lessons because they think I'm too childish for them, they also continuously moan about my friends, saying if I got my own place I'd get used by them and they'd just come and live there whenever they want and they won't even let me stay home alone while they go on holiday or anything.