Automatic door! I lost so many chickens due to forgetting to close the door at night until I got one. Haven't lost a hen since I installed it. I have the pullet-shut chicken door with a light sensor and solar charger for the battery. It swings open like a regular door. There are guillotine type ones (door drops down) out there too, but I didn't have space for it. i also love my sand floor, but it doesn't count as something I wished I had installed. I started with a sand floor. It's over wood flooring. I did recently cover the wood with hardware cloth so rats couldn't eat their way through it. It's taken them several years to figure out that they could, so I guess it's another thing I should have installed when I built the coop.