An easy way to enhance the look of any diesel locomotive is to blacken the grills and vents to provide more depth.  You can use a black wash to bring out the grill or vent details.  Weathering powders are extremely effective bringing out locomotive vent and grill details.

Hopper Weathering Clinic II
By Bill Mock
December 2009

So here's how those BN Hoppers turned out after the surface rust dried. Not bad. I'll [ ... ]

For the TL;DR - just scroll down an look at photos is useful since it's about architecture :) Feedback appreciated !

I want my layout to have a high level [ ... ]

 This is Micro trains Line SD40-2 Santa Fe model which I customized with working ditch lights.