I normally do my paintings, especially my watercolors, from the top down, and from back to front. I have reached the point here where I am at the plane of the side of the house, so I've begun assembling the bricks from the top down. I am not yet too concerned about cast shadows, but the color intensity will lessen as I work my way down. I also like to paint bricks in a patchwork, first to give them variety as the water/paint ratio changes as I go, but also to avoid painting wet in wet and having one brick's paint bleed into another.