I created this shelf to clip on to the $10 filament shelf (https://www.thingiverse.com/thing:465371) so that the filament shelf could hold more than filament. One of the cool ways to print this is without top and bottom layers (see image) and with 10% gyroid infill. Without these settings the shelf is a little bit flexible but still plenty strong and you save a lot of print time and filament. I've printed this in both PLA and PETG.