Expecting variable error with a button


I have a code for a menu system. I can’t see what’s wrong but it keeps telling me my first if statement is wrong it is expecting a variable not a type. Can anyone help me?

using UnityEngine;
using System.Collections;

public class Menu : MonoBehaviour {
	public Texture MainMenuBackground;
	public Texture PlayButton;
	public Texture QuitButton;
	// Use this for initialization
	void Start () {
	// Update is called once per frame
	void Update () {
	void OnGUI() {
		GUI.DrawTexture(new Rect(0,0,Screen.width,Screen.height),MainMenuBackground,ScaleMode.StretchToFill, false, 0.0f);
		if (GUI.Button(Rect(10,500,500,300),PlayButton)) {
		if (GUI.Button(Rect(50,700,500,300),QuitButton)) {

Try : if (GUI.Button(new Rect(10, 500, 500, 300), PlayButton)) {