Deploying a WordPress website to Google AppEngine is something documented by Google itself.
Anyway, this guide illustrates you in details all the steps you need to take to have a WordPress website up and running on the Google’s Platform, integrating this procedure into the bigger one of the continuous deployment of WordPress websites and extensions.
Please, if you like, feel free to comment with links or instructions that you think are useful (all comments, obviously, will be patiently and meticulously evaluated).