Arches need to have a separate row of bricks defining the curve- usually turned 90 degrees from the ones in the wall part, so you see their ends. . . then make the thickness of the wall equal to one brick length. . . does that make sense? The way you have it would be both difficult to build and weak- which may be what bothers you about the shader- it doesn't match what an arch looks like in reality. Also you have some bent bricks in the corners- really only noticeable in the closest one. Bricks might be a bit large- what scale are you going for? Markd