Check out how simple is in Photoshop to make buffalo check(gingham, grid) tileable and seamless pattern in couple color variations. Final results: http://www.greenafik.com/buffalo-check-pattern-adobe-photoshop-video-tutorial.html
If you don't know: in 0:27 copying by dragging while holding alt key
and in 1:16 opening Blending Options by double clicking on layer.
