If you can't wait for official Android 4.4 KitKat ROM to arrive for your Nexus 7 then we have a solution for you all. Developer at XDA have managed to create a Android 4.4 kitKat based ROM for you all. If you want to install it then follow this simple guide given below.
If you have 2012 model then download your ROM from here
If you have 2013 model then download your ROM from here
Download Google Apps from here
To go to recovery mode download this app from Play Store
Then Wipe data in the recovery mode. After that click on Install button and select install from Zip option. After all this reboot your device and Hence you have Android 4.4 ROM on your Nexus 7 tablet