I had an idea the other day when trying to think of a costume idea for my friend. You could do it.

For each costume, break it down into its components.

Clark Kent: black glasses, superman t-shirt, fake press pass, black suit. (Basically just tags)

Then allow someone to input all the random crap they have laying around their house and you can tell them which costumes they can create from that random crap.

It's like an ingredient based recipe search engine, but for costumes. http://allrecipes.com/Search/Ingredients.aspx