Problem with minimap

I make a minimap(camera and emptyobject) for my game .I have no problem in game mode in unity , but if i build and run my minimap map is doesn't exist. My script C# : using UnityEngine; using System.Collections;

public class GUIManager : MonoBehaviour {

 public RenderTexture MiniMapTexture;
 public Material MiniMapMaterial;
 private float offset;
 public Texture MiniMapRama;
 void Awake () {
     offset = 10;
 }
 void OnGUI () {
 if(Event.current.type == EventType.Repaint)
 Graphics.DrawTexture(new Rect(Screen.width -200 - offset,offset ,180,180),MiniMapTexture,MiniMapMaterial);
 GUI.DrawTexture (new Rect (Screen.width -200 - offset,offset , 180,180), MiniMapRama);
 }

}