Good day.

Today I present to you my newest creation (though it's already about a month old by the time I post it here), a PvP arena. I built it almost completely out of nether materials.
It was designed for up to eight players and consists of four layers. Once you fall down to layer two, you can't get back up to layer one. The layers get smaller the lower they get, and the most effective way of killing someone has proven to be knocking him/her off the platform where he/she will fall to his/her brutal death in hot lava.

The arena has dimensions x=31, y=92, z=31. It was originally built inside a hill, so I suggest you do that too ^^
It can be played in two ways.
One, the vanilla way: Flick the lever to release all players at once. Every player can get into his cell by using the half-finished lobby on top of the arena. I'll leave it to you to finish the lobby because it has to suit your needs, not mine.
Two, the Bukkit way: Use a PvP plugin to set eight spawnpoints, one for every cell, and block off the holes made for vanilla users. Any hungergames plugin should be capable of doing this.

Important Note: If you use the schematic the whole arena will be pasted BELOW you! Make sure to at least be at y=93 to avoid parts of the arena being cut off by the world boundary.

Please don't reupload this arena anywhere. Neither in it's current nor modified form. Other than that you can do whatever you want.

Additional Notes

Texturepack used for the first four screenshots: Sphax PureBDCraft
http://bdcraft.net/