Not only do ruined buildings add atmosphere to a gameboard, they also influence visibility and provide cover in game-technical terms.
All these come out of my ‘debris box’.
An MDF or plasticard base, covered with sand and shredded plastic and styrofoam and broken models, then sprayed with a base paint to fixate all that stuff.
They’re given a basic shade and highlight job and some details like destroyed wargear are picked out.
Battlefield eye-candy goes along well with these models.
The ruin pieces are all unique items.