What flowers you add is totally up to you and your color palette. I'm going to quickly fill in with light pink chrysanthemums so you can see how different it can look with different flowers.
Keep the flowers fairly short and low on the top. Again, remember to keep your guest's line of sight open so they can enjoy the wedding ceremony.
Don't be too perfect in spacing out the flowers. Cluster some heads a little closer together for a more casual, plucked from the garden look.
Keep the framework of your greenery in mind, following it with the insertion of your flower heads.
Very quickly, a few mums adds a new dimension to the design!
Look from the sides. You want a dimensional look - yet you don't want to intrude on your wedding aisle space! You don't want to catch the flowers up with your wedding dress on your trip down the aisle!
For a little more variety, I've added a few blue thistles into the mix, filling in open holes with this secondary flower.
Now let's move on and see the same greened cage and how it looks with vibrant red roses!