Draw borders cube

There is a answer that draws the bounds using Debug.DrawLine(). Substitute your favorite line drawing solution:

http://answers.unity3d.com/questions/461588/drawing-a-bounding-box-similar-to-box-collider.html

Actually I already tried this solution. Works perfectly in editor, but I didn't figure out how to convert this to GL. Here my attempt:

 //Attached to objects (cubes) 
 public class ShowMeshBounds : MonoBehaviour
 {
     private Vector3 v3FrontTopLeft;
     private Vector3 v3FrontTopRight;
     private Vector3 v3FrontBottomLeft;
     private Vector3 v3FrontBottomRight;
     private Vector3 v3BackTopLeft;
     private Vector3 v3BackTopRight;
     private Vector3 v3BackBottomLeft;
     private Vector3 v3BackBottomRight;
 
     private Vector3[] list = null;
 
 
     void Update()
     {
         CalcPositons();
     }
 
     void CalcPositons()
     {            
         if (list == null)
         {
             list = new Vector3[24];
 
             Bounds bounds;
             BoxCollider bc = GetComponent<BoxCollider>();
             if (bc != null)
                 bounds = bc.bounds;
             else
                 return;
 
             Vector3 v3Center = bounds.center;
             Vector3 v3Extents = bounds.extents;
 
             v3FrontTopLeft = new Vector3(v3Center.x - v3Extents.x, v3Center.y + v3Extents.y, v3Center.z - v3Extents.z);  
             v3FrontTopRight = new Vector3(v3Center.x + v3Extents.x, v3Center.y + v3Extents.y, v3Center.z - v3Extents.z);  
             v3FrontBottomLeft = new Vector3(v3Center.x - v3Extents.x, v3Center.y - v3Extents.y, v3Center.z - v3Extents.z);  
             v3FrontBottomRight = new Vector3(v3Center.x + v3Extents.x, v3Center.y - v3Extents.y, v3Center.z - v3Extents.z);                  v3BackTopLeft = new Vector3(v3Center.x - v3Extents.x, v3Center.y + v3Extents.y, v3Center.z + v3Extents.z);  // Back top left corner
             v3BackTopRight = new Vector3(v3Center.x + v3Extents.x, v3Center.y + v3Extents.y, v3Center.z + v3Extents.z);  
             v3BackBottomLeft = new Vector3(v3Center.x - v3Extents.x, v3Center.y - v3Extents.y, v3Center.z + v3Extents.z);  
             v3BackBottomRight = new Vector3(v3Center.x + v3Extents.x, v3Center.y - v3Extents.y, v3Center.z + v3Extents.z);  
   
             list[0] = (v3FrontTopLeft);
             list[1] = (v3FrontTopRight);   
             list[2] = (v3FrontTopRight);
             list[3] = (v3FrontBottomRight);    
             list[4] = (v3FrontBottomRight);
             list[5] = (v3FrontBottomLeft);
             list[6] = (v3FrontBottomLeft);
             list[7] = (v3FrontTopLeft);
             list[8] = (v3BackTopLeft);
             list[9] = (v3BackTopRight);
             list[10] = (v3BackTopRight);
             list[11] = (v3BackBottomRight);
             list[12] = (v3BackBottomRight);
             list[13] = (v3BackBottomLeft);
             list[14] = (v3BackBottomLeft);
             list[15] = (v3BackTopLeft);
             list[16] = (v3FrontTopLeft);
             list[17] = (v3BackTopLeft);    
             list[18] = (v3FrontTopRight);
             list[19] = (v3BackTopRight);
             list[20] = (v3FrontBottomRight);
             list[21] = (v3BackBottomRight);
             list[22] = (v3FrontBottomLeft);
             list[23] = (v3BackBottomLeft);
             Camera.mainCamera.GetComponent<DrawLineBounds>().cubes.Add(list);
         }
     }
 }

 //Attached to Camera main
     public class DrawLineBounds : MonoBehaviour
     {
         public List<Vector3[]> cubes = new List<Vector3[]>();
         void OnPostRender()
         {
             GL.PushMatrix();
             GL.Begin(GL.LINES);
             GL.Color(Color.blue);
                 foreach (Vector3[] lista in cubes)
             {            
                 for (int i = 1; i < lista.Length; i++)
                 {
                     GL.Vertex(lista[i - 1]);
                     GL.Vertex(lista[i]);
                 }
             }
             GL.End();
             GL.PopMatrix();
         }
     }

There is a nice grid-drawing script here on Answers, I used it myself with some customizing. You can use it to draw a whole 3d grid, 2d grid, single slice of a 3d grid, or even a single cube, you just need to dive into the code and change the coordinates :)

http://answers.unity3d.com/questions/482128/draw-grid-lines-in-game-view.html