This works for the RPI 3B+. I haven't tested any other models.

Additional Parts:

     2 M3 screws (not too long otherwise they may collide with the extuder)

Assembly:

• Attach the bottom of the case with the screws as shown in the picture

• Place the Raspberry in the case
• Close it with the top

My Print settings:

• Printed in PETG with 0.15 mm layer height. 
• Supports only for the big opening in the bottom part. 
• First layer of top part printed with half speed.
• Infill : 50%