Welllll...maybe not exactly designing full-scale theme parks but rather work for people who do stuff for theme parks, etc. Also, I like to come up with ideas for rides, attractions, etc.
Through a friend, I was given an opportunity to design concepts for a backyard project, for a "very well to do" client, on a scale would resemble a theme park. The theme they wanted was "if Indiana Jones had discovered a Mayan civilization that was invaded by pirates...". Cool, eh?
Here are some of the concept pieces I drew up: