What do I wear to a wedding that's in Chicago during November?

I believe the wedding is inside, but I’ve only been to weddings in spring or summer, and I’ve only been to Chicago during the warm months of the year. Right now I’m not sure what I should wear that will be warm and appropriate to a wedding.

Any ideas/links for suggestions?
I don’t own too many dresses, so I’ll probably be buying something for this occasion.