What are the measurements to a PS3 game case?

If by PS3 game case you mean the PS3 Game console Dimensions the Sony USA site described the PS3 120 GB Slim as Approximately 11.42" (W) x 2.56" (H) x 11.42" (D) (290mm × 65mm × 290mm) see related link

If you want a size for some cases of the new games purchased at Walmart and Gamespot they were 5 3/8 by 6 3/4 by 5/8 inches or 13 1/2 by 17 by 1 1/2 CM. The Video store resales came in their cases which were larger and measured 5 3/8 by 7 1/2 by 5/8

Try looking at these sites:

An exact answer to your question lies here:

http://boardsus.playstation.com/playstation/board/message?board.id=ps3&message.id=2874587

This is a detailed analysis by Sony of it's case and the insert inside it

www.sonydadc.com/files/am/files/blurayinsert.pdf

A template for making PS3 cover inserts:

http://forums.cdcovers.cc/showthread.php?t=214137