So early this morning I was checking through the various woodworking forums and a fellow was looking for a plan for a step stool. Someone else provided a link to a stool with two steps including the top. (How many steps would OSHA say there are?) but he was looking for one with three steps. It was a simple task to model the two stepper and then modify it into 3 steps. I think this is something that may get overlooked by many users of SketchUp. In much the same way as you can try variations of your own design, you can modify existing projects to suit your needs. There's no reason to re-invent the wheel, then. In the case of this step stool The additional step is a copy of the first one. The parts are all components so they are easily copied. Only the front to back stretchers needed to be modified and that required a Make Unique step before editing.
Inspecting mirrors is a job I could easily see myself doing.