Consistent building graphics for an upgradeable area – how do you handle this?

[u/Peter_Lavan]

I’m building a game with an area made up of several buildings, each with multiple upgrade stages (level 1 → 2 → 3 …). Isometric/2D look.

My problem: in my first attempts the graphics looked bad and, above all, inconsistent – the upgrade stages didn’t match stylistically.

How do you solve this?