Vector3 currentPosition = new Vector3(0, 0, 0);

for (int x = 0; x < width; x++)
{
    float lastZ = 0;
    for (int y = 0; y < height; y++)
    {
        var instance = Instantiate(tilePrefab);
        instance.transform.position = currentPosition;
        currentPosition += new Vector3(instance.transform.localScale.x, 0, 0);
        lastZ = instance.transform.localScale.z;
    }
    currentPosition.x = 0;
    currentPosition.z += lastZ;
}