I bought a 5" Touchscreen LCD on Amazon (http://amzn.to/29gIOQ1) for my Pi3 to use w/ Octoprint. I couldn't find a 5" enclosure with the PI as this board's a backpack and has to connect to the PI's GPIOs, So I made one.
In the picture, there's no holes in the backpiece and I drilled 3 holes as that was an initial bottom piece. The uploaded STL has the holes as well as more room for the cables to come out of the side.
I may keep tweaking this and upload a future version, but for now it works :D
If you wish to tinker/remix or change anything, I made the OnShape doc public @ https://cad.onshape.com/documents/a4faa6f2d264a8ec9f4df769/w/f85371d54d1a29c4ea40f717/e/fdc62bb2a37ddcff73fc5d67
Whats important is 3 shells and 3 top/bottom layers. These are thin pieces so you want that strength.