#include <GUIConstantsEx.au3>
$hGUI = GUICreate('WinSetOnTop')
$nCheckBox = GUICtrlCreateCheckbox('Поверх всех', 10, 10, 100, 20)
GUISetState()
While 1
Switch GUIGetMsg()
Case $GUI_EVENT_CLOSE
Exit
Case $nCheckBox
WinSetOnTop($hGUI, '', BitAND(GUICtrlRead($nCheckBox), $GUI_CHECKED))
EndSwitch
WEnd