I have to do a small 3 tier wedding cake the bride said only to feed 50 people shes wanting it to be round on top, square in the middle(not of set) and another round for the bottom.... What sizes would i use for this? thank u in advance

something like this
http://cakecentral.com/gallery/794483

This cake serving chart might help you in deciding what size pans you need or want to do for the cake.

http://www.earlenescakes.com/ckserchart.htm

HTH...

According to the industry standard Wilton chart:
http://www.wilton.com/cakes/making-cakes/baking-wedding-cake-2-inch-pans.cfm
a 9" round (32 servings)
and a 6" square (18 servings)
would yield exactly 50 servings...
top it with whatever round size 1st anniversary tier that fits for them to freeze.

Thank y'all for the help.... If i was to do a 6 inch round and a 6 inch square on top of each other would that work?

One thing I've done is to get creative on the HEIGHT of the tiers. If you did a 10 inch round double layer cake, an 8 inch square SINGLE layer cake, and a 6 inch round double layer cake you will get a little closer to your 50 servings. You don't always have to do double thickness tiers! The double layer cake tiers will be around 4 inches tall and the single layer tier will be about 2 inches tall. I made a baby shower cake I did where I had 3 tiers and different thicknesses- it's the onesie cake in my profile.