using UnityEngine;
using UnityEditor;
public class MultipleObjectsToLayer : EditorWindow {

static int selection = 0;
static bool includeChildren = true;

[MenuItem ("Tools/Move selection to layer %&l")]
public static void Run ()
{

if (Selection.gameObjects.Length > 0)
{
GetWindow (typeof (MultipleObjectsToLayer)).Show ();
}

}

void OnGUI () {
GUILayout.Label ("Move selection to layer", EditorStyles.boldLabel);

includeChildren = GUILayout.Toggle(includeChildren, "Include children");

selection = EditorGUILayout.LayerField(selection);

if (GUILayout.Button("Move to layer"))
{
MoveSelectionToLayer();
}
}

static void MoveSelectionToLayer()
{
Object[] selectedObjects;

if (includeChildren)
{
selectedObjects = Selection.GetFiltered(typeof(GameObject), SelectionMode.Deep);
}
else
{
selectedObjects = Selection.GetFiltered(typeof(GameObject), SelectionMode.TopLevel);
}

foreach (GameObject go in selectedObjects)
{
go.layer = selection;
}
}
}