I have a potential bride that wants a square 3 layer (offset stacked) cake to feed at the max of 50 people and she plans to keep the top layer...what sizes should I use to make it look proportioned?? Oh and it is a beach theme, we are still working out the details but it will of course have sand and shells! ANy help would be appretiated...and what should I charge, she wants a lot of detail!!

use a 2 or 3 inch difference between sizes...which will give a good space on which to arrange your seashells etc. Using the seashell molds available in most craft stores in the candy making section, just make sure to dust the mold with LOTS of cornstarch before pressing in the strengthened fondant (or gumpaste - whichever you are using).... For sand you can use golden brown sugar, and sprinkle....
The topper on the cake I did (my posts - the blue one) with two baking shells (real ones) - I just pressed the gumpaste between the two, trimming off the excess and, laying on crumpled paper towel to dry....gave a realistic look. (bought the shells in gourmet kitchen shop - for coquille st.jacque appetizers)....
Coloured, and placed on cake using Royal Icing as glue....including the two open shells on the top, I used crumpled paper to hold in place till the royal dried....hid the 'seam' with shells.
'Coral' done with Royal Icing piped onto wax paper, freehand, then stuck with RI 'glue'
Have fun.....it was one of my easiest cakes.....

I did a seashell/beach theme wedding cake for new years eve (posted here on cc). the base was square, the top two tiers were round. all the shells were white candy melts with brown gel paste swirled in. crushed cinnamon grahams for the sand, little fondant pearls dusted with super pearl dust. i did the coral using grape stems and piping over them with RI, and just built it up till it looked like coral. i found a real sand castle on ebay (very inexpensive) for the topper. you can find the castles at mendocinogifts.com they have a real nice variety, they're small, don't weigh much and make perfect toppers.