If I want to order my book in multiple sizes, do I need to create multiple versions of it?

As long as you're ordering the same book style (Classic Custom for example) and the same orientation (square or landscape) for all copies, you can order multiple sizes from a single version of your book.

You'll be prompted to select the book size(s) you want during the ordering process. For example, you can order a 11x9 and 14x11 copy of the same exact book on the same order, but you'll be unable to choose a square (8x8 or 12x12) size of the same book. Similarly, if you create your book in Square format, you'll be unable to order it in the 8x6, 11x9 or 14x11 sizes.