The parts drop rate by citizens, is way too low, it does not keep up with levelling. You level up several times before you get enough parts to expand or increase your inventory size, and by this time you have a whole heap of new businesses that you can't even put out because there is nowhere to put them. The parts needed for expansion and your inventory need to be a lot more consistent in dropping from the citizens, or better still have the parts come from some other regular source than the citizens. It is just ridiculous having to wait so long to expand, if it doesn't change, I will be dropping this game, because it becomes terribly boring when you come to a stalemate and can't go any further.