Well..there is always a good RpG map. If not then something new to a map. I will give you an idea that I had for a defense a while back[I'm not sure if this has been used already] What you can do is make the Supply Depot Built=Invisble Bunker. What I had done was kind of a double defense. Meh..I can't explain it very well so I will put the triggers:
Creates a Marine:
Commands Depot,brings a civilian to 'Marines': Blah blah blah, create bunker, create units, enter bunker, disable doodad state, move bunker, create a pylon.
now if you create a a firebat/ghost:
Commands Depot,brings a civilian to 'Firebats': Blah blah blah, create bunker, create units, enter bunker, disable doodad state, move bunker, create a Photon cannon.
What you have here is a defense of Marines,ghosts/'bats, and of Photon cannons powered by the Pylons.
Does this help some what?