I am making a Princess cake for my niece this month and i really want to make a Princess Fiona 3-d figure from fondant. I have no idea how to. I will greatly appreciate any kind of help.
What I did when I made Remy the rat, is I went to the Ratatouille website and found a bunch of pics of him, left, right, front, etc. as many different angles as possible. Then I just printed and studied the heck out of the pics and started shaping the fondant to look like it did in the pics. If that sounds too daunting, you might consider buying a Fiona figurine to put next to your workspace as you work...she can be your live "artist's model", and then just...go for it!
It seems like she should be pretty simple (LOL famous last words) - I don't mean "easy"! but I mean straightforward: head, body, dress, arms+hands (see some Aine2 videos for help there, esp. with hands and faces). Ears and nose would be glued on separately, for the body you don't have to do much but create a shape that you can drape the dress onto...or better yet just model the body in the dress color and add accents and details on top, i.e. the green "skin" tone at her neck/decolletage and disguising the meet-spot with a nice "border" of the dress. I'd do the hair separately and shape it around your thumb until it can fit over the head like a wig, might be easiest to just make it like a "cap" and groove it with a toothpick, rather than try to get into extruding hair.
The hardest part, I'd imagine, would just be shaping her head so she resembles the real character, and for that I'd just work w/my hands and gumpaste tools to indent the fondant in the proper places. I used the ball tool, the veining tool, and the topside of my fingernails to get the right indentations and grooves.
Oh and use 50/50 fondant/gumpaste, or add gumtex to your fondant, or else you may go nuts with the sagging. Also I used a skewer inside of Remy to support him while he dried. And make sure key pieces are thoroughly dry before attaching them (e.g.: body first, allow a few days to dry, etc.)
I haven't made a Fiona but that's what I'd do as a starting point.
Hope these ideas help, at least a little bit!