Interesting idea, I would have thought all those people working with floorplans would use CAD software. But I guess you could do the same thing in GIS. You would have to make sure you have a watertight data model before you start. I don't see too many problems putting a single level of a building on GIS, or even several levels. But I'm not sure how I would go about those features that connect those levels, like stairs. I'm also not sure how I would model a door to show which way it opens.
I guess it also depends on what you eventually want to be able to do with your floor plans: does it suffice to know Mr. Smith's office is in Miller Hall, 3rd floor, room 302, or do you need to plan fastest evacuation routes etc.? Is the end product a piece of paper or an online application? Who are the users, what level of knowledge do they have or need? How detailed do the floorplans need to be?
Hope these questions and thoughts help point you in the right direction!