For those who need basic & light-weight GUI for their Ubuntu Server, you can do the following:

“sudo apt-get install xorg openbox”

To easily access it via VNC:

“sudo apt-get install tightvncserver”

To start your VNC server, simply type:

“vncserver”

Then you can access this VNC server via any VNC client, such as Remmina with the following server info:

“servername:1” (for the first vncserver, replace 1 by a corresponding number as necessary)

If a password is required and the server didn’t prompt you for it, simply run:

“vncpasswd”

After you’re done, don’t forget to kill your VNC server via the following command:

“vncserver -kill :1” (replace 1 by a corresponding number as necessary)

All the above packages take very little resources from your server, for example they all take around 100 MB of storage only!

Source: https://help.ubuntu.com/community/ServerGUI