|Hi, sorry for the delay but I have been superbusy. Here you go: https://github.com/danielepantaleone/b3-plugin-cod4rotate
I didn't test the plugin since I have no CoD4 server, so please report any bug you find and I'll try to provide a fix (hopefully you find no bug).
You can configure the amount of seconds the server can stay "idle" in the configuration file. Basically the plugin checks for any activity on the server. When no activity is detected for the configured amount of seconds, the map is rotated.