help on countdown timer

i need help on my timer i keep on getting errors
help needed guys…

using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class Timer : MonoBehaviour{

float Timer = 300.0f;

public Text text;
public GameObject GameOverText;
public bool enable;

void Update()
{
	Timer -= Time.deltaTime;
	text.text = "Time Left:" + Mathf.Round(Timer);
	if(Timer < 0f)

	{
		GameOverText.gameObject.SetActive (true);
	}
}

}

Hello , you need to rename : float Timer = 300.0f;
try float Counter = 300.0f instead

If you would like you could just make your timer a radial progress bar, or kinda like a health bar in the upper corner that counts down till zero and then when it hits zero it does something else.