Matthias walks you through the build over at his GitHub page for the project, and it includes the components you'll need, step-by-step instructions and the code required to make it all work. He started with a 70-year-old ancient radio, and with the Pi, a modern amp and some other components, he turned it into a streaming radio that could play his own music right from Google Music or other streaming services. He even wired it all up so the original rotary encoders on the radio would switch stations and inputs, and the lit up numbers on the front indicate which playlist or streaming service he's currently listening to.
Over the course of the build, Matthias admits that his choice of amp left a bit to be desired (although he also explains how he fixed that), so you could always swap it out for one you prefer. He uses jQuery to pull down radio streams and adapted it to support Google Music. It's a pretty impressive build, and while it's not something you can just whip together in a weekend, we can't argue with the results. Hit the link below to see the full build, along with more photos of the finished product.