I'm planning my room but i can't choose a theme?

Most larger furniture stores have free and easy-to-use room planner software applications.

BTW, just 10 days ago, when you were 15 yrs of age you posted this:
http://able2know.org/topic/254595-1#post-5763372

I think you should go for mid 1950's Zambezi Tree House, with shades of Elvis Jungle Room.

Elvis has left the building!

I still root for black and white classy themed room. You say that you have limited space in your room so I also suggest that you should have storage furniture like storage beds and cabinet.

Just stick to a two-tone scheme(black and white). For your storage, you can put two small closets and make your workstation in between. Make use also of the above portion of the desk by adding shelves for your books and other stuff. Also add cushions. Use light colors for decorations. It enhance the feeling of space.

How about off white walls then it will feel very clean? Depends on how much cleaning you do - if you're not going to clean it then go with darker colors!

If you have white furniture then you should go for off white walls or use any other dark color which reflects

Choose white wall color with black wallpapers and black flooring, i think it will look trendy.