I designed the case using an existing model created by the Ruiz brothers. Find a link to that original case guide here.
Download all the 3D files from my Thingiverse page below to get started.
I took the Ruiz Brother's design and added the letters and words with a free online cad software for beginners called Tinkercad. It's seriously easy to use and you don't need any previous experience to learn it.
To edit any existing design, you need an .stl file of the design, which the Ruiz brothers graciously provided from their Circuit Playground Express Case Project.
An .stl file is really just a basic 3D file of the object.
Once you download the .stl file, you can upload the file into Tinkercad and edit it from there!
In Tinkercad you can drag and drop pre-made letters and shapes onto your existing file.
To edit this design, I chose to make the letters holed rather than extruded or sticking out of the case. I did this because when the case is printed, much better results can be attained from the holed letter method as the extruded letters tend to made things more droopy because of overhang. More on that here.
Once you have all your letters and edits in the right place, you can group them altogether which basically cuts the holes where you placed them and gives you one file with everything together.
Select the entire model and all the parts you created and then click "Group" in the top right hand corner.
As for the bottom half of the case I didn't change anything but you certainly can!