Aw, Chicken Run is one of my favourite movies! For the feet, I would start with a base shoe and cover it with the form, using foam fabric, for example. Good luck and don't forget to post photos!
Working on: Anna (Frozen), Hermione (movie uniform version), Marinette (Ladybug)
Future cosplays: Rapunzel, Elyon (blue dress), Astrid (first movie)