Here is an enclosure for an Arduino Uno that I designed in Tinkercad. I have printed it, and it works pretty well, although I really want to rearrange or redo the holes so that they line up neatly with the header pins. It does make a nifty little home for an Arduino, if you have yours sitting on your desk all day like I do.
This thing was made with Tinkercad.
Edit it online https://tinkercad.com/things/goyPxkdQ46U
Print both halves and join them. Let me know if you have problems. Feel free to go on Tinkercad and modify your own version of it - Mark it as a derivative, I would love to see it :)
FYI - this is based off this version which I designed as well: https://tinkercad.com/things/aeeotgSaQ1x-shapely-arduino-enclosure-print
That one should work too - I just printed the bottom half. I wanted to use less plastic, so I made this version. Also the cuts along the snapfit make it easier to get this version open.
I could not have made it without the fantastic work of Mikko's Arduino Box model, which I used for the model of the Uno itself: https://tinkercad.com/things/gj927lPLv2P-arduino-box