What would you do with this space?

I'm having a lot of trouble deciding what I want to do with my room and I was hoping you guys could help me out.

Heres what it looks like: http://imgur.com/a/rxxLX

There's going to be darkish lament on the floor. I was thinking about putting the mattres on the floor next to the window but I'm afraid it might look tacky. I want the room to feel really open and somewhat minimalist. I'm also considering putting a book shelf in and some drawers. And im not sure what kind of curtains I should instal. I want to get a desk that is simple but spacious. My budget is $500