Rooting your handset that runs Android 5.0 might not be such a great idea
With Android 5.0, OTA updates patch the entire system at once. This is done to allow for verified boot, which was added in KitKat. According to the Android website, "this experimental feature helps Android users be sure when booting a device it is in the same state as when it was last used." And not having to go through each file individually does have the advantage of being faster.
One downside to patching the entire system at once is that the signatures won't match on files you've changed. This would prevent any OTA update from working. If you must root your Lollipop powered phone in order to scratch your customizing itch, you will need to flash a clean, stock version of Android 5.0 on your handset before attempting to download and install an OTA update.
source: Android, AndroidPolice via BGR