Spike stops to think if it's worth it to build a fire. The rain wouldn't extinguish it if he build it big enough. It seems the gleegirl didn't believe him about the coming storm. Yes, he could discern the location of the savior of the world, but was unable to tell when it's about to rain. "Well, try not to catch a cold. I'll build a fire for you." walking around he picks up fallen branches and twigs to build a fire. He gathers until he has sizable amount, then builds the fire. Lastly he lights it with his flint and steel before heading of to his tent for bed.