I didn't build one. I'm just sharing for those who'd like to build one v.s. buy one
I did build a sunshade for my i-pad mini.
Used materials: 1/2mm photocardboard, black gaffer tape, sheet of pre-glued velvet.
I made it out of 3 pieces. I didn't use tabs or glue, but I used gaffer tape instead.
The top and the back is a folded panel. the side panels are separate.
The inside I lined up with black velvet.
A rectangular opening at the top to let the holder trough.
It is more then sturdy enough for normal use.