The course you choose is another factor that controls the character of the event and how it is run. Normally there will be a reasonable gradient so that the carties can roll from the start to the finish though gravity alone, although this is by no means mandatory. There are several successful events where the carties are pushed some or all of the way.

Generally speaking, the course you have will be pretty much fixed, since it is some local feature that naturally lends itself to the idea of a soapbox cartie race. In fact it is often the inspiration for the event in the first place. There are usually several things you will need to do to the course to make it safe for competitors and spectators alike, and also other options - such as chicanes and slalom sections - that you might consider to make things more challenging.