Every Star Rating has a certain chance of appearing. The 5 Star Rating is the highest in the game, so it has the least chance of appearing randomly, compared to other ratings. However, we’re sure that Lady Luck will smile upon you – keep spinning!
If you want a guaranteed increase of the level of a building, or if you need to do it right now, you can always use the Lucky Star or the Set of Stars to instantly increase the rating of the building by 1 or 5 stars, respectively.