xpecting (, found 'OnGUI'

You are missing a '}' above your OnGUI(). You do not have a closing '}' for your Start() function. Note in Monodevelop, you can position your cursor next to a '}' or a '{' and it will highlight the matching brace.

Yeah I'm sorry about that. Here it is again, thank you so much.

  var cols:int = 4; // the number of columns in the card grid
     var rows:int = 4; // the number of rows in the card grid
     var totalCards:int = 16;
     var matchesNeededToWin:int = totalCards * 0.5; // If there are 16 cards, the player needs to find 8 matches to clear the board
     var matchesMade:int = 0; // At the outset, the player has not made any matches
     var cardW:int = 100; // Each card's width and height is 100 pixels
     var cardH:int = 100;
     var aCards:Array; // We'll store all the cards we create in this Array
     var aGrid:Array; // This array will keep track of the shuffled, dealt cards
     var aCardsFlipped:ArrayList; // This array will store the two cards that the player flips over
     var playerCanClick:boolean; // We'll use this flag to prevent the player from clicking buttons when we don't want him to
     var playerHasWon:boolean = false; // Store whether or not the player has won. This should probably start out false :)
     
     function Start()
     {
       playerCanClick = true; // We should let the player play, don't you think?
     
       // Initialize the arrays as empty lists:
       aCards = new Array();
       aGrid = new Array();
       aCardsFlipped = new ArrayList();
       
       BuildDeck();
       
       for(i=0; i<rows; i++)
       {
         aGrid[i] = new Array(); // Create a new, empty array at index i
           
        for(j=0; j<cols; j++)
            {
              var someNum:int = Random.Range(0,aCards.length);
              aGrid[i][j] = aCards[someNum]; 
              aCards.RemoveAt(someNum);
         }
       }
     
     
     function OnGUI () //***THE ERROR SHOWS HERE***
     {
         GUILayout.BeginArea (Rect (0,0,Screen.width,Screen.height));
         BuildGrid();
         GUILayout.EndArea();
         print("building grid!");
     }
     
     function BuildGrid()
     {
         GUILayout.BeginVertical();
         GUILayout.FlexibleSpace();
         for(i=0; i<rows; i++)
         {
             GUILayout.BeginHorizontal();
             GUILayout.FlexibleSpace();
             for(j=0; j<cols; j++)
             {
                 var card:Object = aGrid[i][j];
                 if(GUILayout.Button(Resources.Load(card.img), GUILayout.Width(cardW))) 
                 {
                     Debug.Log(card.img);
                 }
             }
             GUILayout.FlexibleSpace();
             GUILayout.EndHorizontal();
             }
             GUILayout.FlexibleSpace();
             GUILayout.EndVertical();
         }
     class Card extends System.Object {
         var isFaceUp:boolean = false;
         var isMatched:boolean = false;
         var img:String;
         
         function Card(img:String)
         {
             this.img = img;
         }
     }
     function BuildDeck()
     {
         var totalRobots:int = 4; //we've got four robots to work with
         var card:Object; // this stores a reference to a card
     }
     
     for (i=0; i<totalRobots; i++)
     {
     }
     
     for(i=0; i<totalRobots; i++)
     {
         var aRobotParts:Array = ["Head", "Arm", "Leg"];
     }
     for (i=0; i<totalRobots; i++)
     {
         var aRobotParts:Array = ["Head", "Arm", "Leg"];
         for (j=0; j<2; j++)
         {
         }
     }
     
     for (j=0; j<2; j++)
     {
         var someNum:int = Random.Range(0, aRobotParts.length);
         var theMissingPart:String = aRobotParts[someNum];
         aRobotParts.RemoveAt(someNum);
         card = new Card ("robot" + (i+1) + theMissingPart);
         aCards.Add(card);
         card = new Card ("robot" + (i+1) + theMissingPart);
         aCards.Add(card);
     }