 <p>Roslyn is two things:</p> <ol> <li>An API that lets you see "compiler things" like syntax trees and symbols.</li> <li>A new csc.exe that is implemented atop #1.</li> </ol> <p>If you want to make <em>changes</em> to the compiler and use that to build, take a look at <a href="https://github.com/dotnet/roslyn/blob/master/docs/contributing/Building,%20Debugging,%20and%20Testing%20on%20Windows.md">these instructions</a> if you haven't already. There's a few different ways you can make your own version of csc.exe and then use that to build something. But there's no "choice" dialog like you're looking for.</p>