I made these for a 3A+ build that I wanted to put a fan on, but thought I'd try to get a little creative with the fan's grill. I wanted to use the spots where you would normally put stickers for the serial number and what-not. The first one I did was the Space Invaders theme, but I wasn't happy with the fidelity of the print for the sprites, so I re-did it with pac-man, and I think that one came out better, given it's mostly a lot of dots anyway.
the fan I used was 30mm x 30mm x 7mm, like these. It fits tightly and the fan holds it in place, so glue isn't neccessary. There is a bit of a lip in the inside-pi-side of the model, to help keep wires and stuff from hitting the fan.
this is a finished print, but i had started sanding it down some to see if I could get a smooth finish, that i could coat with clear-coat, but I think it actually looked better un-sanded, with the print lines visible.