Checking and warning users about maintenance

I'm working on this project that will have a lot of maintenance and updates. What I want to do is something like happens on those MMO Games: When the system is going for maintenance, the game displays a warning with a countdown, then users can finish what they're doing and logout.

I will set a flag on the database or maybe even on the web.config file. Then the system needs to keep checking for this change and auto开发者_运维问答matically shows a div with a countdown and some info.

I'm using a MasterPage, so there might be a start. Any Ideas?

The MasterPage would be the perfect place to put that countdown, you will have to check your database for the flag, on every request, and when found display the message on your master page, you could add some javascript on the client side to make it look cooler, by picking up the time and counting down to zero, seems you already have your answer, any specific issues?