I chose to go with a pretty unique design. I build a creeper statue on a little island I built in the water (since nothing strikes more fear into a minecraft player's heart), made it into an entrance structure and viewpoint, and I'm in the process of building the arena in the water beneath it.
The entrance is located under the creeper's torso, leading straight up into the head. From there, two separate ladders are available, one for competitors and one for observers.
I filled the space in the torso between the ladders with lava and made the shafts with glass for a cool aesthetic effect. Down the warrior's ladder, there are chests for safe storage of any inventory items and a chest filled with non-enchanted arena legal diamond weapons and armor. Then the warriors enter the arena, and the observers enter the deck.
My goal is to have two arenas stacked on top of each other. The first will be a melee arena made of bedrock for durability. The second, located beneath, will be a glass arena (observation deck excluded) above a pit of lava, where a game involving bows will be played, the winner of which drops his opponent into the lava by breaking the glass or shooting him dead.
Once the whole thing is done I'll upload a couple pics of the project.
