[Van]

There are a ton of good ideas mentioned so far. I would suggest you try the one that appeals the most to your shop and artistic capabilities. I hate the idea of destroying real books, it's just a thing of mine. The idea of cutting of the spines then gluing them onto a piece plywood is one way I've seen it done. Another way I've seen it done is to get real books and cut out the center of all the pages, to reduce the weight, or replace the pages of real books with foam. As someone esle pointed out, remember that there are several "stock" sizes of foam and stacks can be made out of layers of varying sizes. A one inch thick piece of foam can be carved, with a "sureform", very easily, to appear as a the spines of several books, then just cut the top edge to appear as differeing heights of books. Hope that helps.