I've made shadow boxes as wedding gifts for my sister, my sister-in-law and several friends. I include the wedding announcement/invitation, a picture of the couple and then I try to incorporate the flowers and colors they use in the wedding. I usually line the back with white or black satin and leave bunches and gathers to catch the light. They sell white, black and wood framed shadow boxes at Hobby Lobby in several sizes for a reasonable price. Here are some pics of the one I made for Ginger.
Here's one I made for my sister-in-law's friend. I just did white toile flowers since I didn't know her colors and I threw this one together pretty quickly.