Best way to go about duplicating and inverting rooms?

Hello, I’m currently making an apartment level, and the floor plans of each neighboring apartment are inverted (along the X axis). What would be the most efficient way to design this way? I’m currently blocking with BSP, and if it was possible to basically highlight all the walls and floors in Apartment (A) and then simply invert them to create the Apartment (B) floor plan and then move it into place, it would make things a whole lot easier. I tried duplicating (alt>drag) and then -1’ing the X scale but for some reason it just causes all of the brushes to become invisible and almost mimic a Subtractive brush instead of just reversing the walls. Could anyone give some advice on a good way to do this? Thanks.