The best starting place for the tree is a book that is slightly taller than it is wide. This one is 9 inches by 6 inches. For the angel, a square book is best. This one uses a book that is 7 inches square. You could also use a book that is wider than it is tall, but you’ll need to cut the pages along the outside edge so they are the same width as they are tall. That way they will form perfect triangles when folded in half diagonally.