Stepping Through an animation using script?

I'm trying to make a building that will progrss toward completion as it is given resources. I want to make an animation for its being constructed and then have it be further along in that animation as it is more complete. I cant just make the animation take as long as the building takes to build because the progress may go at different speeds, stop, or go backwards. I figure that it must exist because the car setup seems to use it for steering. So can anyone tell me how this would be done?