Optional Base Defense if playing with biters. Lv 3 Adds dragons teeth and roboports for automated repair. It's ok if you do not have robots yet, just don't remove the ghosts and they will be placed once you get to that point (just remember to repair yourself until then). Lv 2 and Lv 3 Defenses can be placed at any time after Lv1, split up to make initial resource sink easier and ability to have defenses in place faster given how late I have it set to go in.