I use cheapest tools and materials found at the craft store.
Then I paint rubble with burnt umbra and walls with a mix of yellow and white paints. At this stage I use cheap paint from craft store.

After it's dry I highlight the walls with pure white acryllics.

Then I wash the walls with a watered-down brown umbra mixed with glaze medium.

When it's dry I add damage with black acryllic marker, highlight all the rubble and paint all the graffiti etc.
Here are the painted walls:


