Help! I want to do my paper on Gothic Architecture, but I need to get specific!?

The paper has to be 10 pages (double spaced) so it has to be a topic with a lot of info. I also need 5 sources (non-internet preferred). I really want to do it on Gothic Architecture, but I need to be more specific. I've been to the Salisbury Cathedral, so it'd be especially awesome if the topic included something about that. Thanks!