When making an Ogham cloth, there are no specific rules to follow as far as size or color. I generally make my cloth 30"x 30" wide. I personally prefer the color blue. But your cloth can be any color you choose. The four symbols for thr three Queens and the king can also be any color. They are generally embroidered onto the cloth.
For the 3 squares that represent each of the three realms, I generally take a piece of black border and sew that right to me cloth. I do the same with the X that breaks the realms down into each quadrant.
If you like you can put holes around the edges of the cloth and then thread a drawstring through. In this way you can place your fews into the cloth and draw it up as a pouch which can be hung from your belt or staff.
Feel free to decorate your cloth in whatever manner appeals to you. Make it unique to you.
When making fews, I generally will take some1"x 2" strips of wood (flat trim works well) and paint the Ogham letters onto these. I then coat them with a couple coats of lacquer.