Until now, Google has only made the factory images for the Nexus 5 up for download. The company will make the factory images for the other supported Nexus devices available for download, once it starts rolling out the OTA update over the next few days. 

However, since Google has already pushed the source code of KitKat to AOSP so developers can start cooking ROMs for various Nexus devices, which don’t require any closed source binaries.

First Nexus device to get the AOSP based Android 4.4 ROM is the Wi-Fi version of the new Nexus 7 (2013). Installing the ROM requires your device to be rooted with a custom ROM installed. If you already meet the above requirements, head over to this Rootzwiki thread for the download link.

If you have a custom recovery installed on your Nexus 7, but don’t know how to install a custom ROM, follow this guide. There are no proper Google Apps package available right now, so you will have to wait for at least a few hours before someone uploads a working GApps package for Android 4.4.

Update: A semi-working Google Apps package can be downloaded from here.

Update 2: An AOSP made Android 4.4 ROM for the 2012 Wi-Fi model of Nexus 7 is also up for download now.

Update 3: Here is an installation guide to help you in installing the above ROM.