I'm doing a wedding cake for a friend and she is wanting a 12' square, 10' circle, 6 hexagon. She wanting fresh roses around each layer but I'm not sure how many I would need I'm not wanting to buy to many or not enough. Can someone please help me thanks

It really depends on how big the roses are. Obviously with the biggest roses you will need much less of than minature roses.
Measure the cake pans' circumferance with a tape measure and the width of the roses you are buying and divide the pan size by the size of the roses. If it doesn't turn out as a whole number round it up.
Do that for each cake and dont measure the circumferance of each pan and add them together before dividing by the size of the roses.

In any case get a few extra in case of mishaps!