Hi, I don't know if this will be a good solution for you, but when I have multiple design options for one building I use the renovation Filters.
I make the base of the design, or whatever part of the building is not going to change as I will normally do, then I create a new Renovation Filter for each design option I'm going to have, duplicating the Show all filter.
Later I select the new created filter and click in the "Show on Current Renovation Filter only" button. When this option is selected all elements you draw will only show when that specific Filter is selected. This give you the possibility to make a lot of design options within one file.
But watch out the file size, if is getting heavy I would recommend doing more than one file.
PD: The "Show on Current Renovation Filter only" button is the one highlighted in blue in the Pic