How do you adjust your plans?

Hey all,

I'm looking for plans for a bookcase/display case, for some collectibles that I have, but also I am just running out of room for my books and records at the moment. I've found some plans, but they aren't as deep as I'd like. (I have a large action figure collection, and one thing I'd like to display is a wrestling ring I have which is like 22 square inches. And most bookshelves cap at like 12"/14". Are there any places that help adjust plans or any good rules of thumb to follow?