How to map out and run an encounter set in a predominantly vertical area online?

Upcoming in one of my D&D 5E games, the player characters are going to have to venture down a dwarven mineshaft while being attacked by dwarf zombies. The shaft itself is an entirely vertical pit, with layers of stairs and scaffolding around the edge creating a path to the bottom.

I’ve researched into ways to do this, including this question here, and I would be happy to attempt to build a 3D model of the terrain, however the issue is that the game is entirely online. Usually for maps, we’ve used Roll20 which offers a nice top-down 2D perspective, and I can get some limited 3D out of it by placing things in layers. However, this method is already clunky, and with how tall the shaft is going to be… it’s just really not gonna work.

So that leads me to my question, what are some ways I can represent this vertical area and it’s associated encounter in an online-friendly way?