A graduation cake!

So I've been asked to make a graduation cake to feed 200 people on SATURDAY!  AHHHHH!  I of course said yes, this poor mom has WAY too much on her plate to make her try to find some one else. So I'm thinking of making a sheet cake with a book on top.  I've never really done cakes, so this will be interesting!  I didn't charge much just because I don't know how it's going to turn out.  I hope it turns out well!  I'll bake the cakes on Friday night and then decorate Saturday.  Wish me luck!