You can never have enough terrain pieces.
The building ruins are made mostly out of cardboard, they are glued on to a masonite board that I broke the edges by hand instead of sawing it to get a little rougher edges. After the cardboard was attached I applied sand and rubble on the ground and on the inside of the building. Next step was to prime it with black and after that a sort of "zenith light" priming with dark grey.
After that I teared of bits and sides of the printed paperbuildings you can find at Hawk Wargames homepage and glued it on the outside of the buildings.
By tearing instead of using a scissor I get an uneven edge.
Next step is to glue some more sand on the front side to cover where the printed paper ends.
And finally I used black acrylic paint diluted with lots of water to let the natural colour variations on the sand shine through.
They are far from perfect but for the amount of time it takes to make them they are great.
It would be nice to be able to have an whole city like these in the future.
Here are some of my previously made ruins.