Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:3555117.
I had printd a back cover for my Galaxy S5 but it took some damage so I decided to print a new one. Since the first one had some minor problems printing I decided to design my own. First I designed a basic phone shape with as exact measurements of my phone as possible and then created the cover relative to that model. You can use the phone model to design something around it.
Galaxy_S5_Basic_Cover.stl is the cover with minimum necessary cuts. Galaxy_S5_Cover_Chamfered.stl has some chamfers added. This is the model that I printed. Galaxy_S5_CheckCoverFit.stl has most of the cover cut So it is a faster print to check how will it fit your phone.
If you need to adjust the clearance or the thickness of the cover use the two marked spreadsheet cells in the FreeCAD file. You will have to adjust the Chamfer edges because of present (10.04.2019) topological naming issues in FreeCAD.
Any comments, suggestions, tips,... are welcome and apreciated :) Please post your makes :)
Edit 2019.12.15: Just for clarification - the green case in the photos is printed/sliced from Galaxy_S5_Cover_Chamfered.stl with the settings below. The pattern in the center is actually gyroid infill.