The case is not difficult to print but it will test how well you have your machine tuned. If you look at the reprap forums, you will find lots of people posting pictures of vases, yodas, and other irregular objects to show off their printers. The one thing all of these have in common is that they hide systematic error in your printer. In my opinion, the single greatest test of a 3D printer is a vertical face with perpendicular through holes. When you print something like this, any problems with the pitch and consistency of your z-axis, mass of your x carriage and bed plate, and tuning of your speed/acceleration will become very obvious. You will find that you will be able to print a usable case very early on, but you will probably spend some time getting the hang of your machine and fine tuning your print settings before you are completely satisfied. The fine tuning is the most enjoyable part to me, and also how you learn the most about subtle mechanical design features of the printer and their relation to print quality.
Let us know if we can be of any help.