In my opinion, the boss battle should flow as following:
Boss attacks:
Alternates between different ways of attacking the players, which require them taking cover in different places. No single spot should be safe from all attacks, to keep the players moving.
Boss has an enrage timer, at which point it simply obliderates everybody
Boss sends out a laser array to scatter the players at certain damage intervals. This ensures that players can't stay in one place and attack, and causes them to panic
Boss could use rockets, pipe bombs, lasers, sentries, minigun bullets, melee and sentries installed in the arena.
Boss destruction:
Blunt damage
certain weak spot (ala golden wrench)
finding and destroying power towers in the arena
Players fight the boss by moving between cover, assessing attacks, destroying power cores. When all of the power cores are disabled the boss's shield goes down for 60 seconds while they are repaired. Once the boss has been damaged enough, it opens up a weak spot for players to attack, finally destroying it. Am I taking this too seriously?