Timer / popup gui help

Hi,

I am new to AutoIt.

I am working on automating some functionality for a web app. When a specific web page opens I want to display a gui for the user to select several options that will be passed to the web page. I am unclear on how to have the gui "hidden" and only show up when the active page is on the monitor. I am thinking that this needs to be done on a timer but I am just not sure how to go about it.

For testing I see this being the code to open the GUI:

Func WaitForNotepad
    If WinActivate("Untitled - Notepad")Then
        GUISetState(@SW_SHOW)
        Return
    EndIf
EndFunc

In this case I want the gui to show when the active window is Notepad. But how do I get the script to "sleep" until notepad is open.

Thanks in advance.