What is the best way to realize a floor system for a top-down game?

Let’s say, I want to have a building with multiple floors. Because I’m making a top-down game, I can’t just allow top floors to be visible at all times, because they’ll be obstructing camera view.
Right now, I have system, that allows hiding objects if they’re not at the same floor as the player character. However, their appearance and disappearance are too rapid.

I have a few ideas how to approach this problem:

  1. I can make stairs usable objects, so player is just being teleported on different floor while screen fades out.
  2. Don’t use stairs at all, only elevators. However, it’s not really a good option, since using elevators drop gameplay pace drastically.
  3. Find a way to fade out objects on upper levels.

About 3: I know I can use materials or material instances to change the opacity of objects but making mat instances for ALL objects on the level is just too time consuming. Is there another way to change opacity of an object without changing all materials by hand?

I have a master material for everything that will need to be masked, and then just use material instances with parameters for whatever needs I have. I have tree leaves/bark and flooring so far that share the same master material.

Yeah, that makes sense. I’ll try and look into master materials. Thanks!