We have a tool called "jhbuild" that keeps track of all the dependencies and stuff. In short, just get jhbuild from git.gnome.org, build it and do a "jhbuild bootstreap && jhbuild build".
More complete instruction can be found in the wiki: https://live.gnome.org/Smoketesting
If you want to just check out gnome-shell without the other Gnome 3 stuff, you can find instructions on http://live.gnome.org/GnomeShell