Soak a 3- or 4-inch cube of florists foam in water, then place it in the center of the cake stand on top of the moss. The saturated foam anchors the arrangement while keeping the flowers hydrated.
Trim your rose stems to 2 inches and insert into the top of the foam cube, creating a tight cluster that overlaps the edges. Tuck succulent rosettes around the foam.
Continue adding succulents until the sides of the foam cube are concealed. Cut the succulent heads as though they were flowers, making sure to anchor the stems in the foam, if necessary, so the rosettes face outward.