Development for the LG G Flex is on fire. Few days back, we got hold of CWM and TWRP. Now, we have the root instructions for it. First get vroot from here and install it on your computer.
Connect your G Flex phone to your computer. Make sure you have activated USB debug on your phone. Start vroot and click ROOT, wait phone to reboot itself. It will now disconnect from computer. Download clockworkmod superuser from playstore on your phone. Launch it, and update binary.
Now, download Titanium backup (full version) from playstore. Stat it. Kill all open apps. Now, launch Titanium backup and freeze Vroot. It is at the end of the list. Relaunch clockworkmod superuser and re-update binary and reboot the device. Now you can uninstall Vroot using Titanium Backup.
That is it. You have successfully rooted your LG G Flex.