Oh yes, big screens with green lights always instil a nice warm fuzzy feeling. Plus it means you can turn the lights off and pretend you're in a Doctor Who episode.
Easiest approach might be to make it a web site with a simple front page containing just traffic lights and which click through to more info. So, your big screen just shows the front page but if it goes red anybody in the office can get the page in their browser and then click through to find out exactly what's wrong.
Definitely recommend keeping it simple - forget lots of explanatory text, just the colours are good. Nothing more annoying than squinting at a distant screen to try and see whether things are OK. I would also strongly consider a way to show historical results (not necessarily on the front page) so you can tell how long something's been failing and whether it's failing consistently or flapping. Worth noting that existing monitoring systems such as Nagios will do a lot of this for you, but in an irritatingly mediocre fashion. You might like to read this post for some alternative views.
If you find yourself with failover scenarios, where you have a backup system which cuts in while you perform upgrades to a master, then it's useful to also have a failover monitoring system. Once you've done the upgrades you put the failover system monitoring the upgraded primary and check that everything is green just before dropping it back into service. Not sure how applicable to PA that is, though - it's not as if you can run instances of everyone's web apps on a backup system before putting it live. It's worth thinking about if you ever have master/slave scenarios where failover is part of the upgrade process.