Should be fairly straight forward to print. I've had good results without supports but you may need some just for the side cutouts.

Can be easily customized by removing top and bottom layers, increasing wall count and playing with the infill to make a pattern you like. 

I've printed them out of PETG and TPU and have had pretty good results. You can try with PLA, but I find it to be too stiff to put in the phone without the case cracking on one of the corners.