Personally, I'd do it in rolled fondant (ready roll icing, or you can make your own - it's dead easy, plus nicer and easier to work than the bought stuff - I can give you a recipe if you like). Only thing is, if you want to colour it, you need to use paste or gel food colouring, as the liquid stuff will just make it sticky and nasty. You also need to have the cake at room temp, and don't put a fondant-covered cake in the fridge, as the fondant can sometimes weep). To ice with rolled fondant, you need to crumb coat the cake with a thin layer of buttercream, then roll out the icing (not too thin) on cornflour, and just lift it over with the rolling pin and smooth it down. A ribbon round the bottom of the cake will hide any scruffy edges. Once you get the hang of it, it's dead easy to use. You can paint it and everything. Will bung a picture of a butterfly cake I made recently on my profile, if I can find it.
Littlefish, I basically use this one but I use a whole 2kg box of icing sugar, rather than the 8 cups specified, and I substitute 4 leaves of gelatin for the powdered stuff. I think I used spreadable butter instead of vegetable shortening last time too. Makes lovely icing.