Thanks for the help, but I've find another way to do it. I've given a texture (with a bump) to the wall class of the massing model and this simulates a façade to the massing model. It looks pretty great but now I've come across another problem. I tried to simulate a balcony which works, but the problem is that the texture (with the balcony) also appaers in the roof and the floor of the massing model, even though the roof of the massing model is set on a different class (with a different texture). Does the wall class of the massing model include every surface of the massing model (roof, walls, floor)?