Indydebi is correct....make sure you have proper support in your tiers or otherwise you are flirting with a disaster!

That said, here is a good recipe that I use all the time for tiered cakes:

FUDGE CAKE

Heat oven to 325 ºF.

Grease and flour a 9 x 13 pan or two 8 inch layer pans (line layer pans with parchment or waxed paper before greasing and flouring...I use Pam for Baking).

In a small saucepan, combine:

1 cup water
1 teaspoon instant coffee
½ cup cocoa
2 sticks butter

Bring to a boil, then cool to room temperature.

In a mixing bowl, combine:

2 cups self-rising flour [I use White Lily]
¼ teaspoon baking soda
2 cups sugar [1 cup brown and 1 cup white]

Blend well to combine.

Pour cocoa mixture over flour mixture and mix on low until blended.

Add:

2 large eggs
½ cup buttermilk
1 teaspoon vanilla

Mix on medium speed one minute.

Pour into pans. Bake until cake tests done with a toothpick.