So far the Slums is the only building I've noticed this on but there could be others in the future. When you mouse over the building on the build mention and it list the cost of the building the last part the number of spaces it uses does show up because it would be outside the window. This really isn't a big deal but for later with more buildings likely to have increased building cost there is a pretty good chance that they will suffer from this same issue with items on their cost not being visable.
