Update: Dont worry, the project still continues. Though I have scrapped the old "arena" shape and implamented a new one. The name "Semi-Sphere" still applies though (as you will find out on the last level or two).
I have everything that I need to actually finish the Arena shell now (including all the air locks and such. The main "gates" are done, I just need to put them back together and copy + paste them back into the map.
No screenies to show as of yet (its all in peices). As soon as I have the Gates constructed I will show them in action.
So far the gate testing is going pretty well. When the gates open a combine shield is in place that only allows the units comming out of the airlock to pass. In this way the player + co, ant lions and zombies cant wonder into the air locks and bugger them up (that was my main concern really).
Stay tuned.