I think that one of the most challenging spaces to design sometimes is a teenager's room. Most often children want a more grown-up, "teen" room somewhere around the end of 5th grade (aka start of middle school). The challenge is designing a room that still looks youthful without looking too childish, all the while still retaining enough maturity that they can grow into the space as they move on into high school and college. Add that to the fact that most teens want to voice their opinion on the way their room looks, and sometime you can have quite a test on your hands.
I have created an inspiration board for a teen girl's bedroom:
I tried to make the room girly and fun by using soft colors. I also tried to retain some youthful elements in the funky lamp, curtains and by framing the fun perfume prints for the walls.