This Barbie Birthday Cake was made for a friend's daughter.
Butterflies: Ahead of time, I tinted some Wilton gumpaste light purple, rolled it out thin, cut out small butterflies using a cookie cutter, and then propped them in a V shape to dry.(I tilted a square cake pan up a bit on one side, lined it with wax paper, and then put the butterflies in place, resting one wing on the bottom and one wing on the side of the cake pan.)
Roses: The roses were purchased from my local grocery store in the cake decorating aisle.
Small flowers: I used the Wilton Floral Garland Cutter / Ejector Set, which made it very easy to make lots of little flowers in a short time period. They are made of fondant (with dots of frosting as centers), but you could also use gumpaste.
Bottom tier: Is a 12" round cake, iced with regular frosting. The ruffle boarder is done using a leaf tip and going back and forth with it, so that it slightly overlaps itself.
Skirt: I baked the skirt in a Wilton Wonder Mold pan. Iced it with regular frosting, and then placed irregularly shaped and sized "logs" of fondant (tapered so they narrow at the top edge) vertically on the skirt to make the folds of her dress. Covered the whole thing with a circle of pink fondant. Piped on the ruffle on the bottom edge of the skirt -- I think I used Wilton tip 104, but it's been quite a while ago, so I don't remember for sure. Sprayed the top lightly with red canned food coloring, to get a slightly varied color.
Bodice: After putting a doll pick into the skirt, I made the bodice of pink fondant. To get the shape at the top, I used a special cutter designed to cut fondant borders, but you could get a similar effect using a scalloped rolling fondant cutter, and cut it into a gentle V shape. I sprayed the top edge lightly with the canned red food coloring, and then also painted on some sparkle (I think it was Wilton silver luster dust, applied sparingly, but I'm not certain.) I cut a purple "belt" in a similar way as the top edge of the bodice, to hide the join between the doll and the cake, and then decorated it with a few small flowers. (NOTE: be sure to roll your fondant pretty thin, or your doll will appear chubby.)
Misc: The hair band is just a thin piece of fondant, embellished with a flower. The cake board was covered with a shimmery piece of wrapping paper and then clear contact paper. I used a hot glue gun to attach the flowered ribbon, which I got at a craft store. By the way, I always use at least 2 layers of the thin cardboard cake circles for my cake boards, making sure that the corrugations run in opposite directions, so that it will be stronger.