How to build lattice screen?

I want to make my own lattice screen but cant work out the mathematics of how much timber etc. I'm going to put it in the garage roller door to allow better ventilation under the door when it is open (also keeps the cats in.) All the prefab stuff is 2400mm wide. My door is 2500mm wide, so therefore the need to make my own. Think I would like to have some kind of plan before diving in, instead of going back to the hardware again and again until i have enough timber. The specs would be 2500 wide by up to a meter high. Suggestions...?