public GameObject pre;

    public int counter = 0;
    public int worldWidth = 20;
    public int worldHeight = 20;

    private float positionX;
    private float positionY;

    void Start()
    {
        chessBoardCube = Resources.Load<GameObject>("Prefabs/pre");
        positionX = -11.24f;
        positionY = 4.8f;
        counter = 0;
    }

    void Update()
    {
        for (int x = 0; x < worldWidth; x++)
        {
            for (int z = 0; z < worldHeight; z++)
            {
                if (counter % 2 == 0)
                {
                    GameObject block = Instantiate(pre, Vector3.zero, Quaternion.identity) as GameObject;
                    block.renderer.material.color = Color.black;
                    block.transform.parent = transform;
                    float xP = positionX * 3;
                    float yP = positionY * z;

                    block.transform.localScale = new Vector3(2, 2, 1);
                    block.transform.localPosition = new Vector3(xP, 0);
                }
                else
                {
                    GameObject block = Instantiate(pre, Vector3.zero, Quaternion.identity) as GameObject;
                    block.renderer.material.color = Color.red;
                    block.transform.parent = transform;
                    float xP = positionX * x;
                    float yP = positionY * z;
                    block.transform.localScale = new Vector3(2, 2, 1);
                    block.transform.localPosition = new Vector3(xP, 0);
                }
            }
            counter++;
        }
    }