Here is the UnityScript implementation of the method i use to generate a randomly tiled background, the problem i'm having relates to how to translate the call to the newTile method in c#, so far i've had no luck fiddling... can anyone point me in the correct direction?

Thanks

#pragma strict
import System.Collections.Generic;

var mapSizeX : int;
var mapSizeY : int;
var xOffset : float;
var yOffset : float;

var tilePrefab : GameObject;
var tilePrefab2 : GameObject;


var tiles : List.<Transform> = new List.<Transform>(); 


function Start () {
    var i : int = 0;
    var xIndex : int = 0;
    var yIndex : int = 0;
    xOffset = 2.69;
    yOffset = -1.97;

    while(yIndex < mapSizeY){
       xIndex = 0;
       while(xIndex < mapSizeX){

                var z = Random.Range(0, 5);   

                if (z > 2)
                {

                 var newTile : GameObject = Instantiate (tilePrefab, Vector3(xIndex*0.64 - (xOffset * (mapSizeX/10)), yIndex*-0.64 - (yOffset *  (mapSizeY/10)), 0), Quaternion.identity);
                 tiles.Add(newTile.transform);
                 newTile.transform.parent = transform;
                 newTile.transform.name = "tile_"+i;
                 i++;
                 xIndex++;

                 }

                 if (z < 2)
                {

                 var newTile2 : GameObject = Instantiate (tilePrefab2, Vector3(xIndex*0.64 - (xOffset * (mapSizeX/10)), yIndex*-0.64 - (yOffset *  (mapSizeY/10)), 0), Quaternion.identity);
                 tiles.Add(newTile2.transform);
                 newTile2.transform.parent = transform;
                 newTile2.transform.name = "Ztile_"+i;
                 i++;
                 xIndex++;

                }


       }

       yIndex++;
    }
}

C# Version [Fixed]

using UnityEngine;
using System.Collections;



public class LevelGen : MonoBehaviour {


    public int mapSizeX;
    public int mapSizeY;
    public float xOffset;
    public float yOffset;

    public GameObject tilePrefab;
    public GameObject tilePrefab2;

    int i;

    public System.Collections.Generic.List<Transform> tiles = new System.Collections.Generic.List<Transform>();

    // Use this for initialization
    void Start () {

        int i = 0;
        int xIndex = 0;
        int yIndex = 0;
        xOffset = 1.58f;
        yOffset = -1.156f;

        while (yIndex < mapSizeY)
        {
            xIndex = 0;
            while(xIndex < mapSizeX) {

                int z = Random.Range(0, 5);

                if (z > 5)
                {
                    GameObject newTile = (GameObject)Instantiate(tilePrefab, new Vector3(xIndex*0.64f - (xOffset * (mapSizeX/10.0f)), yIndex*-0.64f - (yOffset *  (mapSizeY/10.0f)), 0), Quaternion.identity);
                    tiles.Add(newTile.transform);
                    newTile.transform.parent = transform;
                    newTile.transform.name = "tile_"+i;
                    i++;
                    xIndex++;

                }

                if (z < 5)
                {                   
                    GameObject newTile2 = (GameObject)Instantiate(tilePrefab, new Vector3(xIndex*0.64f - (xOffset * (mapSizeX/10.0f)), yIndex*-0.64f - (yOffset *  (mapSizeY/10.0f)), 0), Quaternion.identity);
                    tiles.Add(newTile2.transform);
                    newTile2.transform.parent = transform;
                    newTile2.transform.name = "tile2_"+i;
                    i++;
                    xIndex++;               
                }

            }
            yIndex++;
        }

    }

    // Update is called once per frame
    void Update () {

    }
}