Addition of Space in the Upper Floor

you can make the second story smaller, the same size or larger and there is no need for the floor plan to be the same for both.

What is needed is a construction type, architect, etc who knows your local bulding codes and the strength of your bearing walls. You tell him what you want and he will find out what the local city permit body will allow and he will see what he can do with what you have.

Quite often cities and towns will not permit some types of structures, so you have to operate within both their laws and the structural mechanics of the house.

I concur with Aurizon.