If you look at my recent blog, it shows some snapshots of a Hunger Games arena I built. I can build you one on your server if you'd like me too! It usually takes me about 10-15 hours to finish it, but it's completely worth it! I usually build them with tubes coming from the sky, and redstone automated doors on the tubes that can be opened from a switch inside the Gamemakers room, along with rivers that can also be shut off from levers in the gamemakers room. Also, the amount of space i usually put inside the arena is huge! It can deffinitly make the game more fun and interesting! :) And there's alot of traps and hidden things, along with hidden chests from the "Sponsors" :)

If you'd want me to build you one, please let me know! :)