What I did to make the holes in the iPhone is to just get a square or any shape, then chose another shape and turn it into a hole then move the hole to where ever you want then group the hole and shape together and done!.
I think the easiest thing for me was making all the holes of the apple logo, the camera inside the phone because I already knew that before when Farshid came before a few months ago. What I found hard was making the inside of the phone case hollow and if I had another chance to make another design I would make a model of a car. I really enjoyed making and designing this iPhone case.