The free SketchUp Make 2017 is ideal for designing spirals or loop-de-loops. The two marble runs you see here were made in about 15 minutes, and are the exact same spiral, just turned on its side with a different wall deleted. There are many good tutorials on YouTube, but here is a good one. Feel free to download the SketchUp file that made the loop-de-loop if you want some inspiration.
A unit of 1 meter in SketchUp is the same as the grid size in Marble Run Maker. This helps you keep your scale correct -- ignore this, and your designs will be far larger or smaller than you intend.
If you intend to build stuff in SketchUp that you can interconnect seamlessly with tracks or treadmills in Marble Run Maker, be sure to build connection points to your objects. For those connection points line up properly, use a square of 1m x 1m in Sketchup as the connection point, and end on even integers. Then any tracks you add in Marble Run Maker will smoothly interlink among your designs. You'll notice that the loop-de-loop and spiral are seamlessly connected to the tracks at both ends.