When using someone else's stones in a commission, there's always a little bit more of a challenge as the stones haven't been selected for what was in mind with the design, the design has to fit the stones.
Diamonds get deeper as they get larger so you need to have a thicker ring if you want to set a larger stone flush into it. However, many people don't like the feeling of a thick ring when it is on.
Here's a shaped wedding ring that I was asked to make using the customer's diamonds. The customer wanted a thin band but wanted all three diamonds set flush into the ring. In order to do this I created a raised section of metal to the exact measurements required to set the larger diamond.
I think the design works really well and makes her ring more unique and special.