Skirmish and/or Customized Game?

[Kreaken]

I haven't personally tried it but I am pretty certain you can set up co-op missions where you play a game such as those that you see in single player skirmish but you can have a team of up to 3-4 players working together to storm their defenses.

Still working on the skirmishes myself in order to get a hang of the game, but I am also curious about how to set this up for future play if anyone knows.