Create a custom selection extension by extending ArcObjects
ZoomToLayerMultiItem.cs
// Copyright 2012 ESRI
// 
// All rights reserved under the copyright laws of the United States
// and applicable international laws, treaties, and conventions.
// 
// You may freely redistribute and use this sample code, with or
// without modification, provided you include the original copyright
// notice and use restrictions.
// 
// See the use restrictions.
// 

using System;
using System.Collections.Generic;
using System.Text;
using ESRI.ArcGIS.SystemUI;
using System.Runtime.InteropServices;
using ESRI.ArcGIS.Carto;
using ESRI.ArcGIS.Framework;
using ESRI.ArcGIS.ArcMapUI;

namespace SelectionCOMSample
{
  [Guid("B8147F77-BE16-4a43-A2F1-E6E030BD579E")]
  [ClassInterface(ClassInterfaceType.None)]
  [ProgId("SelectionCOMSample.ZoomToLayerMultiItem")]
  public sealed class ZoomToLayerMultiItem : IMultiItem, IMultiItemEx
  {
    private IMap m_map;
    private IMxDocument m_doc;

    #region IMultiItem Members

    public string Caption
    {
      get { return "Selection MultiItem C#"; }
    }

    public int HelpContextID
    {
      get { return 0; }
    }

    public string HelpFile
    {
      get { return ""; }
    }

    public string Message
    {
      get { return "Select layer to zoom to its full extent."; }
    }

    public string Name
    {
      get { return "ESRI_SelectionCOMSample_MultiItem"; }
    }

    public void OnItemClick(int index)
    {
      ESRI.ArcGIS.Carto.ILayer layer = m_map.get_Layer(index);
      ESRI.ArcGIS.Geometry.IEnvelope env = layer.AreaOfInterest;
      m_doc.ActiveView.Extent = env;
      m_doc.ActiveView.Refresh();
    }

    public int OnPopup(object Hook)
    {
      IApplication app = Hook as IApplication;
      if (app == null)
        return 0;

      m_doc = app.Document as IMxDocument;
      m_map = m_doc.FocusMap;

      return m_map.LayerCount;
    }

    public int get_ItemBitmap(int index)
    {
      return 0;
    }

    public string get_ItemCaption(int index)
    {
      ILayer layer = m_map.get_Layer(index);
      if (layer != null)
        return layer.Name;
      else
        return "";
    }

    public bool get_ItemChecked(int index)
    {
      return false;
    }

    public bool get_ItemEnabled(int index)
    {
      ILayer layer = m_map.get_Layer(index);
      if (layer != null)
        return layer.Visible;
      else
        return false;
    }

    #endregion

    #region IMultiItemEx Members

    public int get_ItemHelpContextID(int index)
    {
      return 0;
    }

    public string get_ItemHelpFile(int index)
    {
      return "";
    }

    public string get_ItemMessage(int index)
    {
      ILayer layer = m_map.get_Layer(index);
      if (layer != null)
        return layer.Name;
      else
        return "";
    }

    #endregion
  }
}