The outside walls are also taken from the Armoury kit. In this case, I've chosen to resize a plain brick texture for the sides and rear, though it would be entirely appropriate to have graffiti on some or all instead.
The front wall is probably the most heavily-modified piece. It started as a plain brick wall, but I've added 3 door frames from the Armoury's garage, somewhat resized. However, I wanted to make this block look old and tatty and so I didn't want the doors themselves to be identical. 2 are from the Armoury kit, though one has been lightened up a bit. The third door is a texture that I found on the internet and resized & cropped appropriately. I found that searching Google for "metal siding" was the best way of finding such images, though even then it took some effort to find exactly what I wanted.
The sides of the roof are covered with a pattern from a Worldworks kit (can't remember which), somewhat extended and reshaped. I think they were some form of roof edging originally, so they work well for this purpose. The roof itself uses more "metal siding" textures.