CC22 pre-planning: Hogwarts

According to the ICG folks I chatted with this weekend, "Hogwarts" is the theme for the Friday Night Social at Costume Con in April. As I didn't really put forth much effort this past year, I'd like to actually do something this time. Here are the ideas that spring immediately to mind:

• What would a wizard rock star look like? I know that one of the books features a band (Prisoner of Azkaban?) so I'll need to re-read the description. Right now my minds eye is thinking Ziggy Stardust with a pointy hat :P
  
• Snape's sister/cousin/bastard child/etc. An easy one because I'd get to use all black, and it would be an excuse to make his cool black pants with the buttons at the ankle!
  
• A Deatheater (for non-HP folk: a Deatheater is kind of like a Ringwraith, only with worse breath :P) Again, an easy one because it would mostly be a long black robe.
  
• A typical Hogwarts alumni - a variation on something from the movie scenes in Diagon Alley or at the Dursleys.
  

I know that y'all are a creative and clever bunch, so I'm opening the floor. Inspiration including but not limited to the movies. Thoughts?