Leave the chocolate ice cream out at room temp for 15-20 minutes (or heat it in the microwave for 20-30 seconds on low heat) so that it softens and can be spread throughout the pan.
Spread the chocolate ice cream throughout the bottom of the 9x13-inch pan.
Heat the hot fudge in the microwave until it is drizzle-able (30-60 seconds).
Spoon the hot fudge over the chocolate ice cream and spread it evenly throughout the pan.
Place the Oreo's in a gallon bag and use a rolling pin to coarsely crush them. You can also use a food processor.
Sprinkle about 3/4 of the crushed Oreo's over the hot fudge layer, reserving about a cup to sprinkle on top of the finished cake.
Place the pan in the freezer for about 2 hours to set before adding the next two layers.
Take the vanilla ice cream out of the freezer after about 90 minutes so that it can begin softening. Leave it out for 30 minutes and then remove the pan from the freezer to finish the cake assembly.
Spread the softened vanilla ice cream over the Oreo layer, completely covering the Oreo's.
Next, spread the thawed cool whip over the vanilla ice cream.
Finally, sprinkle the remaining crushed Oreo's over the top of the cool whip.
Return the ice cream sheet cake to the freezer for at least an hour before enjoying it.