Yesterday I received an in-game notification that there were two new levels available for me to build. One was a food level (Bongo's Sandwiches), and the other a residential level (Chiss Apartments).
Those were initially not available for building, and I waited until this morning and they were available (presumably due to a bug fix on the developer end).
Just for amusement, I started tapping on other types of floors and discovered that there was a new recreation level (Planetarium), ANOTHER residential level (Talz Apartments), and a new Imperial level available (Blaster Repair).
None of these three new floors provided any notification that they were available for building. I know I didn't miss them being available previously because I have tapped on things randomly before, too without getting new levels.