I know there's a solution for this, because I've seen it in many, many, many maps.. but unfortunately I can't remember which ones, and most of them are locked. (Damn you!)

So, anyways, I want it so that when somebody lifts a building in the zone I have the buildings put, they blow up, then get replaced by a new building of the same type in the same place.

Any answers would be cool, I've been looking for a solution to this, because right now I'm just using a "Lift = You Lose" solution.

Place a location over every building. Then in the location properties unmark the ground ones so it'll only detect air units. Add a trigger which checks if there's a building in the location, if so kill it and create a new one.

Do you mean a Location over every single building, or over all the buildings as a whole?

One for each building. Otherwise you won't be able to create new buildings since those will appear in the middle of the location.

every single building.

To save on locations you can probably make one large air location and one small location. When you bring a building to the air location, center the small location over it, remove it and make a new one. You can open up nearly any defense map and see this in action, and there's numerous threads already on the subject, and a wiki article on it. Granted, the one in our wiki is broken, but you can still use the maplantis wiki for those that are broken.

Thanks man! It worked flawlessy, now.. I have two more problems, which I know you will be able to fix. (Hopefully)

1.) Can I make it so the game does a check of which players are there or not, and will stop the spawn of computers units at the location where his the players base is.
2.) I have the AI on "Random Suicide Missons" so they will attack, but they keep collecting on the bottom of the persons zone, and trying to attack other people from across space.

1) Create the spawn triggers for each player's attacking enemy spawn for that player (so the triggers that create enemies that attack P1 are owned by P1 himself). If that is not possible, tell me and I'll give you another, less elegant, method of doing this.

2) Both "Random Suicide Mission" and "Strategic Suicide Mission" are unstabile each in its own way. Use the 'Patrol to' order to make units aggressively attack to a location.

1.) Worked perfect! The units spawned when Player 1 was active, but when he wasn't there, the units never spawned at his location.
2.) I was using an "Attack To" that was told to wait for 500 milliseconds, the delay was enough to make the game too hard, so I took the delay away and added the patrol to. I will post the results.

1) Either make the triggers which spawn units be owned by the human players only (like JaFF suggested), that way they won't run if the player is not there, or preplace an invincible unit somewhere in the map for each player (a flag or something like that will work fine) and add to the triggers the condition "P1 commands atleast 1 flag", "P2 commands atleast 1 flag", ...

2) Random Suicide Mission and Strategic Suicide Mission will choose randomly the targets from all the units in the map and will order them to attack their target, even if it is not reachable. Order them to patrol or attack will get them to walk to a location and attack there. Another alternative is Junk Yard Dog, they'll move randomly and attack whenever they find an enemy.
It might not work so well but repeating the Random Suicide Mission AI each X seconds might get them to adquire another target randomly. So that might also be an option.

EDIT: Looks like I'm a bit late. Oh well

Yeah, I found that my game became about 100x harder when I removed the Random Suicide Missions, holy cow.. they're vicious now.. got some balancing to do.