I have written an installer using WIX for a product, which uses:
etc.>
Download the WiX latest (weekly) release source code at http://wixtoolset.org/releases and look at the project located in src\Setup\WixBA. The WPF you write will be the bootstrapper UI which references the WiX bootstrapper engine (Burn).
I also created a minimal example that I blogged about here. Please note that it is a bare bones example to get someone started. Using the WiX source as an example is better because it's complete and robust.