Game over?

I have a timer and and when the time runs out I want a button to appear that says time is up, game over, and play again. Im not sure how to do this or where to put it. heres what i have for my code.

[code]

 var isPaused:boolean = false;
 var startTime:float;
 var timeRemaining:float;
 var percent:float;
 var clockBG:Texture2D;
 var clockFG:Texture2D;
 var clockFGMaxWidth:float;
 
 
 function Start()
 {
 guiText.material.color  = Color.black;
 startTime = 10;
 clockFGMaxWidth = clockFG.width;
 }
 
 function Update () {
 if(!isPaused)
 {
 DoCountdown();
 }
 }
 
 function DoCountdown()
 {
 timeRemaining = startTime - Time.timeSinceLevelLoad;
 percent = timeRemaining/startTime * 100;
 if (timeRemaining <0)
 {
 timeRemaining = 0;
 isPaused = true;
 TimeIsUp();
 }
 Showtime();
 Debug.Log(" time remaining = " + timeRemaining);
 }
 
 function PauseClock()
 {
 isPaused =  true;
 }
 
 function UnPauseClock()
 {
 isPaused = false;
 }
 
 function Showtime()
 {
 var minutes:int;
 var seconds:int;
 var timeStr:String;
 minutes = timeRemaining/60;
 seconds = timeRemaining % 60;
 timeStr = minutes.ToString() + ":";
 timeStr += seconds.ToString("D2");
 guiText.text = timeStr;
 }
 
 function TimeIsUp()
 {
 Debug.Log("Time Is Up");
 }
 
 function OnGUI()
 {
 var newBarWidth:float = (percent/100) * clockFGMaxWidth;
 var gap:int = 20;
 var isPastHalfway:boolean = percent<50;
 var clockRect:Rect = Rect(0,0,128,128);
 var rot:float = (percent/100) * 360;
 var centerPoint:Vector2 = Vector2(64, 64);
 var startMatrix:Matrix4x4 = GUI.matrix;
 
 
 GUI.BeginGroup(new Rect (Screen.width - clockBG.width -gap, gap, clockBG.width, clockBG.height));
 GUI.DrawTexture(Rect(0,0,clockBG.width, clockBG.height), clockBG);
 GUI.BeginGroup(new Rect(5,6,newBarWidth,clockFG.height));
 GUI.DrawTexture(Rect(0,0,clockFG.width, clockFG.height), clockFG);
 GUI.EndGroup();
 GUI.EndGroup();
 }

[/code]