You are looking at top stuff here, not average or entry level.
I watched Paul, Brian and a few others discuss station colours for years.
In my view (and minimal experience), there are these ingredients:
- A good idea of what the colours should be. Takes lots of research and/or a few good photos that happen to show the image just the way you want it, so you can steal colour right from the photo.
- A good set of textures for the, err, texture. Like bricks, stonework, wood. There are many sites offering more or less developed raw material. Building your library on these defines the building blocks you can use.
- Either a 3D box with a roof plus lots of work and artistic compromise in a 2D paint programme, or getting the hang of extrusion and subdivision in a 3D programme and doing a little less in 2D.
- An idea on how to get ambient occlusion, i.e., those shadows under the roof. You can bake them in Blender or paint them on the texture. I guess that in terms learning curve and final result, painting them yourself (using some gradient brush or whatever it is called in your programme) might beat the half clever, half automatic stuff in Blender etc.
- Minimal messing with shaders unless you need see-through glass which may be a little harder to set up. But there may well be tutorials on that that I missed.
It is exactly as in cooking. You need to fight down the challenge of getting pasta al dente, rice of the right consistency, etc., i.e., you master a dozen functions in your 3D programme. In parallel, you collect an ever growing of ingredients, i.e., textures that look exactly like you want them to. And a few shelf loads of cook books, i.e., tutorials and hints from forums, plus prototype information.
Whatever you achieve stays with you until you forget it. The building we see here is exactly what the heralded Unreal Engine is made for. So you are looking at the standard for years to come. And buildings are easier to do than engines, because of the simpler shapes.