To build Cinnamon you need base-devel and git.
# pacman -S base-devel # pacman -S git
After that you can install cinnamon with themes and extensions:
yaourt -S cinnamon yaourt -S cinnamon-extensions-git yaourt -S cinnamon-themes-git
Because cinnamon is a fork of the GNOME3 shell you can install the whole gnome package or the packages you need.
# pacman -S gnome
At last you have to add this to your .xinitrc:
exec ck-launch-session gnome-session-cinnamon