The Infrastructure Planning and Design guides (IPD) are always a great resource when working through designs for implementations of all kinds of products and solutions. CUrrently the team is working on the IPD guide for SCOM 2012.
They have released it as a beta version on Connect, giving you the opportunity to read it and react to it.
You can find this beta on the Solution Accelerators connect site over here.
Update 13 November 2012: the IPD has been released.
Enjoy!
Bob Cornelissen