Roofing Tiles

I was after a pattern to represent roof tiles. I've tried the cells pattern before but is was never quite what it wanted. Here's what I came up with...

#include "colors.inc"
camera { location <15,20,-30> look_at <0,0,0>}
light_source{<-50, 100, -50>color White}
background { color <0.25,0.35,0.80> }
#declare myPatt = function(x,y,z){(y - int(y)) - (int(x)/2)};
box{<-10,-10,-10>,<10,10,10>
rotate <45,0,0>
texture {
pigment { function {myPatt(x,y,z)} pigment_map{[0 White][1 Black]}} scale 2 translate <10,0,0>}
}