using UnityEngine;
using System.Collections;

public class showMessage : MonoBehaviour {
    GameObject player;
    private bool  startLap;

    void  OnTriggerEnter ( Collider other  ){
        if(other.tag == "Player") {
            bool = true;
        }
    }

    void  OnGUI (){
        if(bool == true) {
            if(GUI.Button ( new Rect(100, 100, 500, 40), "Help! I lost my car. Find it through this maze for me?")) {
                Debug.Log("Door Works!");
                bool = false;

            }
        }


    }
}

using UnityEngine;

public class showMessage : MonoBehaviour
{
    private bool startLap;

    void OnTriggerEnter(Collider other)
    {
        if (other.tag == "Player")
        {
            startLap = true;
        }
    }

    void OnGUI()
    {
        if (startLap)
        {
            if (GUI.Button(new Rect(100, 100, 500, 40), "Help! I lost my car. Find it through this maze for me?"))
            {
                Debug.Log("Door Works!");
                startLap = false;
            }
        }
    }
}

private bool startLap;
private bool foo;
private bool bar;