About the slums... its a great idea, but we have to think realistically. Yes, slums do exist, but if your the leader of a modern country, if you want your population to grow, do you really think that they would just build a bunch of slums in their biggest cities? I think most leaders ( at least the democratic ones) wouldn't want to shove massive poverty stricken buildings in the center of their great cities just to store new population. I think the more realistic way is to have a building that is more along the lines of a Residential Highrise Project, if you look at Tokyo for example, their running out of room on the ground, so basically their future is moving their populations up. The slums building should exist in some of the larger cities as a penalty, but I don't think they really be a build able city improvement.