I wanted to be able to carry a couple of things along with my phone so I wouldn't have to worry about carrying my wallet everywhere. This case has a little slit that can carry a credit card, drivers license, etc. It also has a little kickstand that let's me position the phone in landscape so the kids can watch an impromptu movie, you can put on the dashboard for GPS, the list goes on and on.
Step 1: First Print All of the STL Files
You're going to be printing a total of ten pieces, two copies of the volume button and one each of all the rest. On my Up! printer is was using 0.2 mm Z, hollow fill, and normal speed (I used fine for the first couple of prints and it's overkill for this project). After you've finished printing clean up any support material and then you should be ready to assemble.
Step 2: Assemble Hinge
I used a bamboo skewer to assemble the back halves. Any rod with a 2.9-3 mm diameter should work to hold together the two pieces. You're basically after something with a tight slip fit so depending on the precision of your printer you're going to potential have to have a smaller or larger rod.
Step 3: Get the Buttons in Place
Get the volume buttons and on/off button in place in the bottom case.
Step 4: Slide the Phone in With Mute Button
After you've gotten the button in place, line the notch on the mute slide up with your phones mute switch and slide both into the bottom case.
Step 5: Top Cover
With the home button sitting on top of the phone put the top cover in place. The use a 2 mm hex wrench to securely fasten all four M3 screws. I used McMaster Carr screws ( http://www.mcmaster.com/#catalog/119/3092/=nblq1p ) but any screw with the same diameter will work to hold the top in place.
Step 6: Assemble Kickstand
The kickstand should fit in the bottom case and should slide in and out with just a little bit of force. The kickstand fits into the card holder piece to hold the phone in landscape viewing profile.