it all depends on the scale, im making a 3 story house in 1/35 and i got a piece of thin wood, cut out the windows, and doors, and all the holes made by artilery, and bullets, paint, add texture with spackle (i use water putty just add water maybe add white glue and u have putty) make floors with balsa, then the interior of the house and there u go!!
blown up houses: do the same thing as above except more holes, (look at a pic) and no interior just A LOT! of rubble
-DJ