This is my take on how to get started designing stages in SketchUp. The video is long, but you should be able to watch it at 1.25x or 1.5x speed (if your device allows it) and still follow along. I believe I covered most of the basics, but more videos will be coming soon that cover more advanced topics and techniques.
Here are the links to download SketchUp and the files I use in the video: