These cases are meant to be printed using flexible filament (eg. TPU 95A - 98A).  

My personal preference is to turn off top and bottom layers and use a 12% honeycomb infill, see screenshot.

Standard versions have 1.5mm sidewalls, Rugged versions have 2.0mm sidewalls.

Slotted versions are for optional kickstand, print the housing and stand in PLA or PETG

Slimfit versions, have back wall thickness equaling sidewall thickness.  Camera bar protrudes unprotected.

Optional grip versions have textured sidewalls as pictured.