Prefab, but you can make 14 layers or so if you are creative and there is a wide range of prefabbed stuff. Not anything like Forza though.
Each game is different and the odds might change depending on loadouts, speed or edurability of enemies, etc.
Tactics and the effects thereof also is relatively random against human or Ai opponents. You can be perfectly organized, but if you don't bring the firepower, or mobility, you could still be toast.
Haha, last time we've played, for some reason the opponents commander came all the way to our base, where I, also commander, was hanging out. Result was a commander on commander battle, which of course was won by yours truly, after which our excelent team, (shoutouts, Twilight, Purg3, Pedro, Kid, Rayne, Scientific, Gibbon, Blackhaw and all the new recruits!) dealt with the rest of the rabble.
This game is crazy sweet online! Sure it has plenty of problems and it's hardly even a well constructed game when it comes to those stupid 'loading lobby' bullshit and lack of proper debriefing, but the gameplay and experience are grand.