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That looks like good work. I have used Sarissa Precision and Warbases mdf buildings for ruins. I usually find I have to add some texture to them to really liven them up .
I like your use of multiple layers to render broken brickwork. Much more convincing than a single ragged edge.
Also on the roof, you probably want to offset the tiles, rather than having them in rows.
Textured brick paper. Not perfect but makes for much quicker builds!