This thread was just pointed out to me after I purchased a Nano Metalfigs set of 20 die-cast Harry Potter figures. Couldn't resist them at only $30. I have no idea what I'm gonna do with them, but here is a pic:
No room on Warrenville for an appropriate castle.
Don't need the castle, just use your imagination for a scene or two and swap the figures out.
Though I recall the bookstore having small Hogwarts buildings you assembled.