Now it's time to fit all of your modifications within the case! This is the step that is often forgotten at the beginning of the process, but while deciding what bends to make you should also have in mind how to fit everything inside the case at the end. Sometimes this might entail moving things around inside the case, or making an external box that gives you more room. But in nearly all cases this will require some modification to the existing case, like drilling holes for switches.
And of course, how you modify the case is entirely up to you--you can give it a new paint job, remove everything and place it in an
entirely different case, and so on. Look on youtube or flickr for some really inspiring examples.