Allow us to define a blueprint which is a building sub-unit (e.g. a section of a wall or a floor of a multi-story building) that can be added to a building being designed. Alternatively, allow us to flag all or a selectable portion of the current state of a building design as a repeatable chunk for copy/paste-like behavior.
Yes, I realize that there are quite a lot of details and parameters to sort through in order to implement this.
No, I don’t expect this to come in the near future.