[header] How to make a very modern room for a teen girl inexpensively [title] Take the girl's tastes into consideration. [step] Though you may assume all teenage girls appreciate similar things, you could be drastically wrong. Ask her what favorite colors, bands, celebrities, hobbies, patterns, and room styles are. 
Get as much information about the girl as possible before beginning. Though not all of it may seem useful, any shred of information can help.