I have been asked to quote for something similar to this cake for an upcoming wedding -

http://www.marthastewartweddings.com/sites/files/marthastewartweddings.com/ecl/images/content/pub/weddings/2004Q1/a100701_spr04_coconutwarm_l.jpg

However it's only to be three tiers and serve around 60 people.

What sizings would you suggest and how many dummy tiers (if any)? Also, if I do have dummy layers, can I coat the foam directly in BC? Or do I need to cover it in something like a cling film etc?

Many people ask how to price their cakes, and the answer is always the same:

how much do your ingredients and materials cost

how much rent, utilities, paper goods, equipment will it use

how much time will it take and what hourly salary are you paying yourself

how far will it have to be driven for delivery

Far far too many variables for any of us to help you with

Here is a chart for sizing.  http://www.wilton.com/cakes/making-cakes/baking-wedding-cake-2-inch-pans.cfm

Most people charge the same or at least similar for a dummy cake as there is the cost of purchasing the dummy to factor in and the the decorating costs are the same.

Thanks ladies.

I should have made it clearer I'm more after answers as to the sizing, and how others would structure it. I'm not sure if I should do a large cake base, and two dummy tiers on top. Maybe 14,12, 10 inch butI'm not sure what would look best as I don't do too many tiered cakes.
 

14, 12, 10 is way more servings than what the customer wants.  I also read a lot that a 6 inch looks best for the top tier.  A 10 inch on top would look very short and squatty.  If you did a 6, 8, 10 you would have 74 servings which the customer would pay for even though they only need 60.  You just can't get exact matches always.  Then you wouldn't need any dummies.

Yeah that's what I thought - it would be short and dumpy with a 14" cake on the bottom, and 12 and 10 dummy's.

Seems all cake is the way to go. Thank you for your help :D