How to Build a "Minecraft Automatic" Chicken Farm
What You Will Need To Make It
A Building Block Such As Cobblestone
4 Glass Blocks
A Filled Bucket of Lava
A Normal Chest
A Redstone comparator
6 Pieces of Redstone
2 Redstone Repeators
2 Carpet Blocks and a half slab
How To Build The Automatic Chicken Farm
Once you properly obtain all of the items above you will now need to find an area that is three blocks wide, six deep and five blocks tall. Next you should start by lighting up the immediate area with torches, glowstone or otherwise luminescent items to properly light the area to stop hostile mobs from spawning.
Step One: The Ground Layer
To begin with the build you will need to place down the chest in the middle of your three wide side. After doing this you will then need to proceed to the rear of the chest and "shift+Click a hopper onto the chest from behind so that the hopper will dump all of the items it collects into the chest. This chest will be where you will obtain the cooked chicken from when your farm is automatically working.
Next you will need to place a building block on either side of the chest on the same level and back five more blocks making it 6 blocks long. Next do this on the other side and then fill in the middle with the same blocks. When you are done it should look exactly like it does in the picture to the right.
Step Two: The Next Layer
To begin the second layer, place a block of glass on top of the chest, to do this, you may have to "Shift+Click" just like you did when placing down to hopper. After that place a building block on either side of the glass block to complete the front of layer one.
Next place a half slab of either brick or stone directly on top of the hopper. This step is crucial because it will create a one half block air space between the block and the lava. This allows the baby chickens to grow up to adults before they are cooked. This game mechanic works because baby chickens can survive in the half slab environment while full grown chickens will have their head directly in the lava, causing them to catch on fire and die.
Following this step, place a dispenser facing the half slab with a comparator set on subtract facing outward. You can tell the comparator is on subtract when the light is on, instead of it being on off on default. This will allow the comparator to send out bursts of redstone power ejecting the eggs from the dispenser rather then a constant flow which would break the machine.
Following that, place a redstone repeat or flowing into a redstone line going left and right and back. The line on the back should flow back into the comparator while the one on the left flows back one block and into a repeater that goes into a building block. Place a building block directly opposite of the dispenser to the one you just placed and you are done with this layer.
The two pictures on the right are what yours should look like at this point.
Finishing The Farm
To start the third layer you will first need to put a block of glass directly above the glass in the previous layer, then place a hopper feeding into a dispenser followed by two more hoppers feeding into the first one behind that. You will also need to put building blocks two high on all the sides and back of the hoppers and glass as shown in the picture to prevent the feeder chickens from escaping. You can then go ahead and put the lava above the half slab. mking sure it doesnt flow all the way onto the half slab.
A Finished Farm
Now you will have to lead chickens into the area above the farm above the hoppers where the carpet should be placed in order for them to start laying eggs. Once an egg is layed, the hopper will collect it and the dispenser and the redstone will shoot the egg onto the half slab where there is a one in twelve chance a chicken will spawn. After the spawned chicken grows up it will automatically be cooked and will be dropped into the chest below.
For more information and help refer to the video below by the farms original creator, the player Xisumavoid.