create maintenance page for non LTM site

Hi,

We need to create a maintenance page for a virtual server that isn't using the LB module (single pool created without LTM).

I need it to load if there is either no response from the actual server due to network issues or if IIS is down or when the site sends a certain response code that will define that it is down for maintenance.

I saw some irules re how to do this but all refer to sites using LB - so, is this the same primciple? How should this be done if we would like to base it also on UI (i.e., access to certain page will trigger the maintenance page, or certain response code as I mentioned above).

Thanks

Vered