If you're willing, Switchboard has an excellent keyboard shortcut configurator built-in.
Switchboard is the "System Settings" app for Elementary OS. You can get the source at the link below and compile for your system according to the instructions in the "INSTALL" file once you extract the archive:
Make sure you have all the dependencies they list in the install file installed before running any of those commands.
ALTERNATIVELY, you may opt to simply install it from the elementary ppa:
sudo add-apt-repository ppa:elementary-os/stable
sudo apt-get update
sudo apt-get install switchboard
Open a terminal and run
whoami. Let the output to this command be denoted
Once installed, navigate to the "Keyboards" section. Then under shortcuts, click on custom enter
pkill -KILL -u <user> by typing it out (no copy and paste) and pressing ENTER.
It will be disabled by default. Click on disabled and then just press the key combination you want to use.
I'm not sure if this method will ensure all your work is saved before logging you out. So please look into this before using it, maybe ask another question here for that.
Although, I'm not sure just clicking on Log Out on the panel ensures your work is saved either...
For more information on this process, see: