When WebFOCUS is actually up and running, but you do not want end-users running content, I put up a default portal page (under each BI portal) temporarily that gives a maintenance message. I then remove it after the maintenance work is completed.
I normally only give access to the WebFOCUS home page to developers, for them, I just send out a message since it is usually a much smaller group.
In some case, where the entire WebFOCUS server might be down, I will redirect the DNS entry for the WebFOCUS server (I use one for access to WebFOCUS versus handing out the actual server name) to another web server with a maintenance message while the maintenance is occurring.