You should use a recipe specifically designed to be a wedding cake as it will ensure that it is sturdy enough and that it makes the right amount of batter and icing. For a three-tier cake, you need to make three cakes of 12", 9" and 6", as well as a massive amount of icing. Most three-tier cake recipes have a step-by-step schedule for when you will need to bake and assemble each part.
Once cooked, leave the cake to cool in the tin. When cool, remove from the tin and place on some baking parchment. Drizzle a couple of tablespoons of brandy (or your other chosen liquor) over the cake and wrap it up tightly in parchment and clingfilm or foil. Every few days unwrap the cake to feed it with another spoonful of liquor, then wrap it back up and return to a safe, temperate storage space.