Ali a couple of ways, depends how confident you are feeling
immediately I'm thinking blue cake with green icing at bottom, few trees, and the gruffalo like the cover of the book, but simplified it honestly wouldn't be that hard,
or do you mean just gruffalo? If you draw out or photo copy pic up to size of cake, that will give you outline to carve, cover cake with chocolate buttercream, score his fur and add face details with fondant, Make on top of the pic to get right size
give me a few more ideas of what you want, must have a google to see what has already been done, and I can give you more help
Friend came with her baby to visit and then PIL came for unexpected visit so didn't get anything else done tonight!