evolution of the evolution of an idea

Following on from the previous post, based on the idea of doing a book in a weekend. I then thought, maybe I could do one book each weekend for the whole month. Four books. Now maybe then they should be tied together somehow - common theme? Suppose maybe the front and back covers could be all parts of the one same image, that work together when arranged side by side. Now that needs a four individual but related project themes. Maybe you have 4 people in your family that you could use - a book on each person? Perhaps you could be one of those people and do a self portrait book? Doesn't work for me but it'd be a way to join the four themed books.