By Request: This is a modified version of my other stand - only this one is for the bare phone without the Ringke Fusion case. See http://www.thingiverse.com/thing:631289 for more details.
This is a generic stand, with a 25 degree tilt, which seems to be the most popular viewing angle. I have added little dams at the ends of the stand which help keep the phone in position.
It didn't win the OnePlus design contest, but it is ridiculously robust and functional. Enjoy!
Put the base flat on the bed. No need for solid fill, something like 25-50% fill should be plenty. I ran it with 4 layers thick walls and it comes out fine. Use a raft unless you are really confident in your platform adhesion characteristics. Typically with something this large, it either peels during build, or is stuck on so hard you end up damaging the edges trying to pry it off.