If you want to put group of computers in maintenance mode in SCOM 2012 you may found a lot of script over Internet on how to do that but it seems Pete’s way is the easiest and efficient one. Read how he did it here.
With System Center 2012 this implementation looks so easy you just have to follow some steps. Pete Zerger provides us with these steps in article titled “Controlling Computer Maintenance Mode in OpsMgr from the Service Manager 2012 Self-Service Portal”.
A nice article from Microsoft Support about what is Maintenance mode and how it works. Find it here.
Very useful article form http://www.systemcentercentral.com titled “Using Orchestrator 2012 to Schedule MMode for OpsMgr Groups”.