Instructions
As Zerg
Spawn drones until you reach 9/10 supply, and then build a spawning pool. Spawn another drone and then an overlord.
Continue spawning drones until 13/18 supply. When the spawning pool finishes, create a queen, two sets of zerglings and an overlord. After the overlord finishes, create another zergling.
Place a spine crawler slightly to the right or left of your hatchery. You want to position it so that it can reach the mineral line and the front of your hatchery. If the zerg opponent is rushing with zerglings, he will likely attack just prior to the spine crawler finishing. Fend off the attack with your queen and initial zerglings. Once the spine crawler finishes, the attacking zerglings should die off quickly.
As Terran
Build a supply depot to the right or left of your ramp once you reach 9/10 units. The supply depot should block the left or right side of the ramp, depending on where you place it.
Construct a barracks at the middle top of the ramp at 12 supply, next to the supply depot. The barracks serves as the main blockade. The front of the barracks should line up with the supply depot.
Lay down another supply depot on the exposed side of the ramp once you reach 12 or 13 supply to finish the blockade. Instead of a supply depot, you can opt for a bunker if you wish. After the blockaded finishes, zerglings cannot penetrate your base.
As Protoss
Place a pylon to the right or left top portion of the ramp at 9/10 supply, cutting of access to the edge of the ramp.
Build a gateway on the opposite side of the pylon. Do not place the gateway directly next to the pylon. Since you're facing zerg, you'll want to build the gateway early, at around 10 or 11 supply.
Create a zealot from your gateway immediately after the gateway finishes. Place the zealot in between the gateway and pylon to complete the wall.
Build a cannon in back of the zealot once the initial zealot is created.Any zerglings that come will quickly die from the cannon and zealots.