This is based on the original by @gjpc but smaller on the outside and (0.1mm) bigger on the inside, to fit my Mini.  This  reduces the thickness of the print to 1.0mm from 1.5, which sort-of works with my iPad case.  Since I did it up from scratch, it doesn't have the nice front lip that the original has.  If you're not trying to fit in into a case, maybe D/L both this model and the original and see which you prefer.

It's a very simple model and I don't think it matters how you print it.  I used PLA, a 0.6 nozzle and adaptive layer height.

Any attribution should be to @gjpc, please.

New 1:  I added a new model that fits snugly over my case, including the protective lip around the edge – see the photos of the gold version. I really like this style, but YMMV. 

Printing tips:

Since the walls are just 1mm thick, aligned seams can cause issues.  I used random seams with a 0.4mm nozzle, smaller layer height and sparkly colour, which hide the flaws from the random seams pretty well.  Also, because of the tight tolerances, any elephant-foot is a problem, so a bit of a raft might be helpful.

New 2:  This should be the last update.  I added a long version that spans the gap between the two speaker openings in the case.  This allows for two small pegs going into those openings to keep the cover from sliding in either direction.  Useful for those of us who never use the camera, but others might want the ability to slide it.  It doesn't cover the ambient light sensor, so no issue there.

Since the long version gets printed upside down and not on it's side, it might be a little weaker (you install it by flexing along layer lines), but there's no issue with elephant foot and I didn't do anything with the seams.