cake drum sizes

Hi , thankyou for letting me join the forum .
i only make cakes for family /friends , i am doing a wedding cake 3 tiers 6.8.10 to be put onto a swan type of cake stand , i am not sure what size drums i need should i use 12, 10. 8 inch or should i use a larger one for the bottom tier , say a 13 inch the cake being 10 inch, any help or advice would be appreciated .