What are some really cool room ideas for a teenage girl that don't cost much or nothing at all?

Your favorite team if you like football, Baseball, Basketball, soccer, hocky, or your favorite tv show like pokemon, avatar, avatar: the last airbender, spongebob, total drama world tour, icarly, big time rush, ect. You can also do your favorite color, or pattern. My sister did her room in light blue and a cloud pattern, to create the cloud pattern use a sponge and make the shape of a cloud. :)