Just use NuGet. The binaries are already there and you'll be sure to get the right stuff. You'll also need a transport package, such as MassTransit.RabbitMQ or MassTransit.MSMQ.
There are instructions on building in the README. If you really want to build from source start there. If they don't work for some reason a more to the mailing list and we can update the README.
Lastly, TeamCity builds MassTransit for you if you want a non-NuGet build, http://TeamCity.codebetter.com. Sign in with guest, find the MassTransit project and you can download the artifacts.