Google Calendar-friendly room reservation system

[misterfriendly]

We have been using Google Apps edu since 2009. One thing that Google Calendar doesn't do terribly well is room requests. We would like a system that simplifies the process of staff requesting room use. Ideally such a system should be smart enough to know when a room is being requested outside of school hours, so that appropriate staff can be notified (facilities, etc) and we'll know who's in the building when, and who's responsible for locking up. We've had a few too many instances of the alarm going off because someone's rehearsal ran late, and the local constabulary are losing their patience with us!

 

Does anyone know of a Google Calendar add-on that will provide this functionality? I do NOT want a separate, stand-alone app that will require staff to remember yet another password.