I've been asked to do my very first wedding cake. It's a very simple design, so that doesn't worry me... what does worry me is that she's asking for a 3 tier cake for between 100-150 people. I can do it for 100 easily... trying to do a 3 -tier for 150 isn't flowing as well... it feels to me like the layers are going to look off. If you were doing this cake what size tiers would you be using.

They are also only keeping 1/4 of the top layer to share for their anniversary.

you could do an 8" 10" and 14" for 140 servings

14" square x 10" round x 6" round = 148 servings.
 

Thank you both so much - This is the cake she wants http://www.bridepop.com/wedding-burlap/a-touch-of-burlap/attachment/mississippi-wedding-cake-burlap-buttercream/ I think we're trying to keep it round. But if she doesn't want to go to 4 tiers I will talk to her about a square bottom to get the amount she wants.
 

A8" 12" 16". Using earlenes chart this is 150

AThis will give you 2" on all sides at the bottom of each tier. If that makes sense.