in the edit menu, select area all floors.
before doing the above command put a cad line(for condos the common wall will represent) to be the plane
you want the mirror should be. don't forget after selecting area all floors to click on the mirror command
which you will find at the bottom of your screen. this appears when you select objects.
that is where you can find, the point to point move(like offset in A.cad),trim,extend, mirror, chamfer,fillet and others equivalent to the modify tool bar in AUTO CAD.