Build time is limited on Boss Gauntlet:

• 1 player - 40 ticks (80 seconds)
• 2 player - 35 ticks (70 seconds)
• 3 player - 30 ticks (60 seconds)
• 4 player - 25 ticks (50 seconds)

And I often run pubs where I have to build everything myself, even with 4 players in the game.  So my variation on this common Boss Gauntlet build is designed to make it faster to build:

1. Only one aura stack in the center.
2. Four minions on hotkeys (archer spider mage orc), so you can build four at once.  Spider and orc aren't better, I just build them because it's faster.
3. Enrage auras are optional but fun.  You can build them if you have time left over, or if you're splitting up building.
4. To save more time, tell the people in your pub to upgrade the buff beams for you once you've placed them.  (Note: 50/50 chance they ignore you when you say this)

Other tips for building:

1. Gas traps and minions should be far enough out that nothing will hit your crystal.  Neither should touch the center circle.
2. Buff beams should be farther out than the minions.  Demon Lord fire can destroy minions, but if it does, you don't want your buff beams to die with them.  I place the north buff straight through the forge, which is far enough out for me, and the south buff is out about the same distance.

Tips on fighting during the wave:

• Kill demon lords first, then goblin mechs, then shoot down the dragon.
• If you stand at the midpoint between two ballistas while the dragon is fireballing, even Super Legendary Monk can run fast enough to reach both of them.
• Don't use a seahorse.  It shoots too far, so it will make it very difficult to trigger the dragon's flame breath.
• When you shoot down the dragon, don't attack unless you can one-shot it.  Stand at the proper distance to trigger flame breath:

Video demonstration:

I screwed up slightly in this video (forgot to bump the east chest as I walked south on EV) so I was a couple seconds short, but there's enough extra time that it wasn't a big deal.