Here is the way for AWN only deskotp environment in gnome 3.

You have to create a new session with awn.
You might need to install gnome-session-fallback

First create a desktop file in xsession with following commands in your favourite terminal:

gksudo gedit /usr/share/xsessions/awn.desktop

In newly open document copy and paste the following and save the document.If you are comfortable with other text editor instead of gedit replace it with your favourite text editor.

[Desktop Entry]

Name=AWN

Comment=AWN only desktop environment

Exec=gnome-session --session=awn

TryExec=gnome-session

Icon=

Type=Application

X-Ubuntu-Gettext-Domain=gnome-session-3.0

If you write Name=AWN, it will be in top of lightdm list and if you write Name=awn then it will be in bottom of list.

Now we have to create a session dock which we have mention in above dock.desktop file. Use the following command in terminal to make it

gksudo gedit /usr/share/gnome-session/sessions/awn.session

copy and paste the following and save it

[GNOME Session]

Name=Dock Session

RequiredComponents=gnome-settings-daemon;

RequiredProviders=windowmanager;panel;

DefaultProvider-windowmanager=gnome-wm

DefaultProvider-panel=avant-window-navigator

IsRunnableHelper=/usr/lib/gnome-session/gnome-session-check-accelerated

FallbackSession=gnome-fallback

DesktopName=GNOME

Here we are using gnome-wm as window manager. Any change in this desktop environment also affects gnome classic session(By change I mean compiz profile). It also loads compiz. You have benefit of it. Instead of gnome-wm you can also use compiz as window manager. While using compiz as window manager you might not be able to log out. You can use Alt+PrntScrn+K combination to log out or if your keyboard keys are not working like mine then you might need a logout script.

But if you are using above examples then there is no problem of it.

Now if you want to have an icon for your awn session in lightdm, then you need a icon of 22x22 pixel png with name custom_AWN_badge.png if you have named your .desktop file as AWN.desktop or custom_awn_badge.png if you have named it as awn.desktop as in above example. Upper and lower case matters. Put the newly created icon in /usr/share/unity-greeter using sudo.

Now if you are unhappy with the result then delete those two files
awn.session and awn.desktop from
/usr/share/gnome-session/sessions/ and usr/share/xsessions respectively.

With Regards...