Another couple questions for my Hawaii beach theme cake. Its going to be for 75 people and it will be two tiers. Will 3 or 4 12" round with 3 or 4 10" round on top be enough? Should I do 14" and 12" instead?

2nd question: The customer would like the sides of the cake to have a rocky finish to it and I've decided that fondant wouldn't be good for that so I was thinking of just doing a "sloppy" greyish buttercream job and maybe painting on some black highlights/shadows. Problem I think I may run into is that I have to deliver it a half-hour away and Im worried that if the buttercream is too thick on the sides it will fall off during the trip? Any advice?

Thanks

I have found a recipe for sugar rocks that I am delighted with. You can make anything from boulders to gravel. It is Earlene's recipe, very simple to make. You can color it any shade, from tan and sandy, to grey and rocky. I used it on my duck cake in my photos on a fondant base. Here is the procedure:

SUGAR ROCKS

Make a royal icing with one fresh egg white and powdered sugar until it is of piping consistency. Whip as much air into this as possible. Color unevenly. For a more natural, streaked effect, don't mix the color thoroughly into the royal icing. Cover with a damp cloth and reserve.

Line a shoe box with heavy-duty foil. Rub Crisco over the interior of the foil lined box.

Melt 4 1/2 C. of white, granulated sugar in 1 C. cold water over a low temperature in a large sauce pan. Bring to a boil and cook to 280 degrees F. on a candy thermometer. Remove from the stove and immediately stir the well-beaten Royal icing into the hot sugar syrup. Pour into the greased, foil lined box, (or a container of comparable size). This mixture's original volume will grow and bubble up, doubling its volume. Let cool completely and then break apart for wonderfully textured rocks. For gravel or fine sand, they can be broken or crushed into small pieces.

I made a couple of batches in different colors, (from sand to gravel to rocks) and have them stored in tightly sealed containers for future use. HTH and welcome.

12" round, 4" high serves 56 1"x2"x4" servings
10" round, 4" high, serves 39 1"x2"x4" servings

So, unless you're planning on serving really big pieces, you'll have more than enough with a 12 and a 10.