In just a few simple steps, we've made significant progress. These additions have added quite a bit if character to the car and have really started to give it some shape. Play with the size of the extrude and also the size of the rounds and the overall design as well as the aesthetics of the car's body will change dramatically.
This is a good opportunity to save as the next items we will get into will most likely result in errors. Multiple rounds and correct sequence of rounds usually result in errors due to incorrect radii or geometry that cannot be created by the software. Any time you ask the software to create a geometry that it cannot create, you take the risk of crashing the software and losing any work you have done up to that moment. As any experienced ProE or Solidworks user will tell you, save and save often. Nothing is worse than completing significant changes and updates and having to redo them due to an application crash. Make it a habit to hit control+s or whatever hot key you have set up.