Minecraft wiki entry for Egg_farming, associated text: The base machinery includes three droppers, a dispenser, three hoppers, a chest, a couple of switches, two redstone repeaters, two redstone torches, and six redstone dust. Making that equipment from scratch will cost a minimum of 6 smooth stone, 15 iron, 29 cobblestone, 10 "logs" of wood (with some bits left over), 18 redstone dust, and 3 string. Also needed are 7 solid opaque blocks, and several that can be opaque or transparent. The chest can optionally be doubled (another 2 wood), and you may well want another chest elsewhere in the egg room, for ordinary storage.
The 9×9 floor inside the room will need 78 additional blocks or slabs (if the optional second chest is used, then at least the space above it needs to be a slab). You may want a trapdoor from the chicken floor to the egg room; the water not only won't flow through the trapdoor, but will generally prevent chickens from slipping down there too.
The pillar will be a slab and another two blocks, one of which should be a jack-o-lantern or other light source. Even a block with four torches will do, but you do need a light there to keep the chicks from drowning themselves at the edges.
The roof will need at least 10 solid blocks to intercept eggs (3×3 over the dispenser, and one topping the pillar). The rest of the ceiling can be filled in with slabs.
The walls should be solid blocks, at least 2 high (the ceiling layer will usually be a third) This will cost most of 80 blocks of stone and/or glass (or 20 wood "logs" converted to planks). Doors can be best placed in the middle of any wall, or all four of them. Given creepers, it's much safer to make at least the floor and the bottom row of the wall out of blast resistant blocks: Any stone will do, as will brick or hardened clay, or even obsidian. This will minimize the mess if it does get blasted, and make it much easier to fix up. Making the top row out of glass blocks lets you see in and out of the farm, which helps avoid creeper blasts in the first place. You can also surround it with other protections such as a moat, which would prevent creepers from damaging the blocks even if they do explode.
If you've been to the Nether, you can add a comparator and redstone lamp, with a bit of dust and maybe a repeater to connect them. This lets you set up a convenient display outside the building, to show when the egger has enough eggs for a full run.