Before Raspberry pi was made there where other boards.
One of them is the Beagleboard i got myself a MX version.
But now day’s you can find lots of cases for raspberry pi.
For the beagleboard this was not true you needed to build your own.
there where sites like http://www.makercase.com/ to make a finger design.
So after getting my dimensions i generated a box and imported the file in to illustrator.
In Illustrator i added the port holes and printed my first test versions: