So this was my first 3d design i did back in 2016 and i published it on Thingiverse (still there). Recently i have gone back and redesigned it to have a cleaner model and also made improvements on the original design with more flavors to choose from so i thought i'd also publish it here because why not :)
There are two main branches of design which basically differ in the way the two halves are fixed together. One uses screws and one is a snapfit design.
Under these branches I added 2 additional flavors to choose from for the top of the case. 1. Normal, 2. with hole for a small momentum switch for power off function. All versions also now have a small hole to fit a 3mm led diode as the power led.
All parts have been test printed to make sure everything fits together nicely (snap fit joints, diode, power switch). For the best surface finish it is highly recommended to print the top part standing upright with the solid sidewall facing the build plate. This way the supports will all be vertical and built on the inside of the top part and even if they leave marks they won't be visible on the outside. Most of the inside will also have a nice surface finish this way. Bottom part you can print flat on its back but you will not get best model accuracy that way because of the curved side lines. Here i would also suggest to print the bottom vertically with supports on the inside of the case. Same with the top half this way you will have minimal support scarring and even those will only be in the inside of the case. Takes a bit longer to print in this orientation but for the better surface finish i say its worth it.
For the Safe power off switch function i used a small momentun switch attach it to GPIO pins 5 and 6. You also need to add a small script to your raspberry pi which does the actual safe power down. You can find it here it here with detailed instructions: https://retropie.org.uk/forum/topic/14537/tutorial-adding-a-dedicated-on-off-switch
For the Power Led i used a 3mm 12V diode. You can get these cheap on ebay or on aliexpress. To connect the diode use GPIO PIN 8 (called GPIO 14) for the positive lead and GPIO PIN 39 (ground) for the negative lead. This way you don't need to add a resistor to the led. Additionally to make this work go to your Raspberry Pi config and enable Serial by going to Advanced Options and enabling it via menu option Serial.