Charlie and the Chocolate Factory
You won't have any trouble with this book. Sure there are some made-up words (whangdoodles, for instance), but it's always clear what they mean. The only things that might trip you up are the puns. Sometimes Mr. Wonka makes jokes that aren't super obvious: you have to think about it for a second before you realize that he's using a play on words. Like when he calls Violet Beauregarde a "Has Bean" (18.48). Think about it. Got it? Yeah.
Other than that, it's a simple story with more or less simple words, so you should be all set.