Sorry my PC died when I was originally working on this and never got it to a playable state. I guess I can keep it here for reference to what I wanted to achieve. A multi-level battle arena. I'm sure it has been done by now though.
Load map using Rocket League Map Loader
(Or rename "Arena_test.upk" to "Park_P.upk").
Run free play training to test it out.
5/9/2016 - Basic structure designed.
5/9/2016 - Added Goals and team colours.