Reasnd constructed this superb ruin using foamcore and cereal packet card however it would be possible to create a similar effect with other materials too.
I began by cutting the main pieces of foamcore from a template which can be accessed here. The template is composed of three basic sections, the front entrance, the side tower main walls, and the side tower filler walls. I modified the front entrance wall section to form the side wall because I wanted to create a stair case leading up this wall to the above ground level; so I didn't want any windows on the ground level. The template indicates cuts with a solid line and uses dashed lines to indicate floor levels and sections that will be glued against adjacent wall sections.
The images below show the basic construction before and after the addition of the staircase and upper floor from scraps of foamcore. Note that at this stage I have not yet created all of the damage that will appear on the final piece however some of it is marked with pencil lines.

The next step was to add detail to the exterior so I used the templates as a guide to cut cereal box cardboard shapes. These were stuck on and I used pins in the corners to hold the cardboard in place while the glue dried. Then I cut some strips of cardboard and glued these on top of the previous layer to give an extra dimension.

I did the same to the side of the building but thought that the empty arches (on the wall that has the staircase) were a bit boring. So, using a ruler, I drew lines for brick work in the empty spaces. Then I cut into the foamboard with a craft knife. The lines were then exaggerated with a ball point pen. At this point the lines were a little too regular for my liking so I just started pushing the pen into the lines in places to randomise it. I'm not sure that the visible brick work is really in keeping with the style of the building, but I do like the effect.
The entire piece was then painted with a textured grey paint (below left) onto which I applied a black wash. Following the application a light dry brush of white to the entire piece for highlighting, I added a bit of brown on the floor.

Before finishing off the painting I wanted to mount the building on a 12" square base cut from MDF to fit in with my other modular terrain pieces. The foundations of the building were cut from a piece of polystyrene foam. Some of the edges were distressed and the offcuts employed as the basis for internal debris. The paving was made by applying squared of cereal packet card. The building was then attached to the base.
I would love to add lots of litter/rubble to pieces like this however this would severely hinder the placement and movement of figures. So, in an effort to maintain the playability of the piece, I restrained myself and just added some minor piles of rubble and left it largely open.
The base was painted using similar techniques to those used on the building which I touched up and drybrushed some walls with a darker shade of grey to add variety.
