I seriously doubt that this would exceed the capabilities of the Greenfoot program. I am not sure, however, that this is what you want to do. Each piece would be an object (not necessarily an Actor object). These pieces can be placed within an array. As you add pieces,, you can recreate the array with the new pieces included, then create a new world from it. The Level class of my Super Level Support Class demo is an example of creating different worlds using specified data within the class. If each piece is actually a separate world in itself (no interaction between the two, my PIP Actor Class shows the capabilities of greenfoot in that respect (the PIP subclass of Actor creates actor objects that can each portray a different world).