I use a free 3-D design and modeling program called SketchUp. This started as an inexpensive commercial product, got bought by Google, and subsequently was spun off to a commercial product again, with a free version. If you Google it you will find the free version. It has a remarkably low learning curve.
SketchUp integrates with Google Maps in that you can accurately geolocate the model you are working on. This means all you have to do is locate your venue like you would in Google Maps, define an area to model on (such as the parking lot and surroundings) and start working in 3-D perspective. It even offers rudimentary terrain information, though unless there is a really significant change of elevation, it's easier if you set that to the flat image.
I have developed a collection of 3-D objects such as cones, gates, turns of various radii, etc. It's not quite ready for public consumption but I will be glad to share it with everybody when it is. Once the design is complete, you can export a 2-D overhead view for use in laying out the course on site, and as a map to be given to drivers.
These are from last year, but here are some samples:
Brandywine Motorsport Club Autocross Chair
AXti.me user since 02 April 2015