I think that factories are too easy to get. Level 1 should require science one and two. Level 2 should require one, two, and three. Level 3 should require one, two, three, and purple science. Recursion 1 should require one, two, three, and purple science. Recursion 2 should require one, two, three, purple, and yellow science. The science required for some of the other things should also change to reflect these changes.

I was also think building level 2 should maybe require concrete to build, and that level 3 should require the new refined concrete, but I'm less sure about that.

If I make factory buildings too difficult to unlock, they'll be too cramped for the things people want to build inside them by the time they're finally unlocked. Where's the fun in putting your production lines inside buildings if the buildings are only available once the production lines are already built and running on the overworld?