Nexus 4 and Nexus 5 smartphones have received an unofficial Android 5.0 Lollipop ROM which allows users to test the latest UI changes and features from Google's latest operating system upgrade. Both ROMs can be found at XDA Developers forum along with other builds that have been made available for the Nexus 7 and Nexus 10 tablets, and for the old Galaxy Nexus model, too.
The Android 5.0 Lollipop upgrade isn't too far away from an official roll out for Google Nexus 4 and Nexus 5, but if you're eager to test it before that happens, then you can choose to flash an unofficial port of Android 5.0 AOSP. In order to install one of these builds you will first need to factory reset your smartphones. Both the Nexus 4 and Nexus 5 ports from Android 5.0 Lollipop are pretty solid and if you're an advanced user, then you should give it a try.
These custom ports of Android 5.0 Lollipop for Nexus 4 and Nexus 5 are packing all the important features such as Material Design UI, new Quick Settings toggles, battery saving mode, Android Runtime, etc. These builds do not contain any mods nor enhancements, so you will be getting full Android 5.0 Lollipop. Note that by installing such ROMs you will also need to completely wipe your devices clean of all files, so that the new operating system will be able to recreate the partitions and install successfully.
The Android 5.0 Lollipop ported ROM for Nexus 4 can be found here at XDA Developers forums, while the one for the Nexus 5 can be installed from here. If you want to install such ROMs on your device, then be sure to check all the info listed there and that your device's battery has enough power in it, so that you will be able to repeat the tutorials in case installation fails at the first attempt.
Remember that these builds are in no way final releases of Android 5.0, install them at your own risk. The official Android 5.0 Lollipop update for Nexus 4 and Nexus 5 should be ready for a November the 12th release, supposedly. Make sure to check our website next week for extra info on the availability of Lollipop OS for various Nexus devices.