The mirror plane has to be one of the planes defined by the center of the object. The negative part of this is that yo can't select the mirror plane. We can select the object we want to mirror, right click on it and select 'Flip Along:' This will give us the chance to select which plane (red, green or blue) of the object to use as a mirror plane.Two of them can be done with the standard SketchUp installation, the third one (and probably the best) requires a Plugin. There are to me 3 methods to mirror objects. Mirror is not a standard tool in SketchUp, but that is probably because there are several ways to Mirror objects using other methods. There are several ways to mirror objects in SketchUp
