[C#] Add information, maybe text, check boxes to a GUI.Box.

I'm trying to add lines of texts, optional suggestions for a game. More specifically, Spades. However, I'm having slight trouble with this. I can't see how to add lines of text, or check boxes to a box in GUI.box. Here's what I have so far:

 public class CameraGUI : MonoBehaviour {
 private int menuSelection = -1;
 private string[] button=new string[] {
     "Single Player",
     "Multi Player",
     "Leaderboards"};
 public GUISkin mainSkin;
 static int startB=25;
 static int buttonW=425;
 static int buttonH=275;
 private int windowW=500;
 private int windowH=600;
 private int screenW=Screen.width;

 void OnGUI() {
     GUI.skin=mainSkin;
     menuSelection=GUI.SelectionGrid(new Rect(startB,startB,buttonW,buttonH), menuSelection, button, 1);
     switch(menuSelection) {
     case 0:
         SPOptionsWindow();
         break;
     case 1:
         MPOptionsWindow();
         break;
     case 2:
         LeaderboardsWindow();
         break;
     default:
         //error handling here....
         break;
     }
 }
 void SPOptionsWindow() {
     GUI.Box(new Rect(screenW*.5f,Screen.height*(.25f/10.0f),windowW,windowH), "Single Player Pre-Start Options");
 }
 void MPOptionsWindow() {
     GUI.Box(new Rect(screenW*.5f,Screen.height*(.25f/10.0f),windowW,windowH), "Multi Player Pre-Start Options");
 }
 void LeaderboardsWindow() {
     GUI.Box(new Rect(screenW*.5f,Screen.height*(.25f/10.0f),windowW,windowH), "Leaderboards");
 }

}