Trouble using C# tooltips

I am trying to make a part menu for my game, and I'm getting 3 errors:

Assets/Scripts/PartMenu/PartMenu.cs(12,94): error CS0119: Expression denotes a type', where a variable', value' or method group' was expected

Assets/Scripts/PartMenu/PartMenu.cs(12,21): error CS1502: The best overloaded method match for UnityEngine.GUI.Button(UnityEngine.Rect, string)' has some invalid arguments Assets/Scripts/PartMenu/PartMenu.cs(12,21): error CS1503: Argument #2' cannot convert object' expression to type string'

Here is my code: using UnityEngine; using System.Collections;

 public class PartMenu : MonoBehaviour {
     
 
 
     // Use this for initialization
     void OnGUI () {
     
         GUI.Box(new Rect(0, 0, Screen.width * (0.25f), Screen.height * (0.70f)), "Part Menu");
         GUI.Button(new Rect(0, 25, Screen.width * (0.125f), Screen.height * (0.1f)), GUIContent ("Small Plate Of Plastic", "Test"));
         GUI.Label(new Rect(0, 50, Screen.width * (0.125f), Screen.height * (0.1f)), GUI.tooltip);
     
     }
     
 
 
 }