I was trying to make this as cheap as possible, so I started with a pack of shims for somewhere around $3 bucks. They are definitely more rustic than what I was going for, but ya get what ya pay for.
I painstakingly cut every piece to a point with a handsaw and miter box. Pain in the butt, but totally worth it. I also made the bottom layer longer than the top layer. To hold everything together, I used a MDF floral ring (found at Michael's. I ended up only using the bigger one).
Before painting, I set it all out to make sure I liked how it looked. Instead of just sticking the mirror on, I wanted it to have a finished look, so I bought a ceiling medallion from Home Depot. I also placed that in the center to make sure it looked ok.
I primed the shims before nailing them on the floral ring. I also alternated them since one end of the shims are thicker than the other. The bottom layer had the thick part toward the center and the top layer had the thin part toward the center.
After it was all primed and nailed, I painted it gold.