色々エラーが出たのでやり方をメモっておく
https://cloud.google.com/community/tutorials/run-laravel-on-appengine-standard

プロジェクト作成

# 5.8を指定してlaravelプロジェクト作成
$ composer create-project laravel/laravel projectName --prefer-dist "5.8.*"

$ cd projectName

app.yaml

instanceを指定せず、デフォルトのF1のままだと展開は出来てもメモリ不足？でエラーが出るのでF4を指定している

app.yaml

runtime: php72

instance_class: F4

env_variables:
  APP_LOG: errorlog
  APP_KEY: YOUR_APP_KEY
  APP_STORAGE: /tmp
  SESSION_DRIVER: cookie

.gcloudignore

.gcloudignore

# This file specifies files that are *not* uploaded to Google Cloud Platform
# using gcloud. It follows the same syntax as .gitignore, with the addition of
# "#!include" directives (which insert the entries of the given .gitignore-style
# file at that point).
#
# For more information, run:
#   $ gcloud topic gcloudignore
#
.gcloudignore
# If you would like to upload your .git directory, .gitignore file or files
# from your .gitignore file, remove the corresponding line
# below:
.git
.gitignore

# PHP Composer dependencies:
/vendor/

コード追加/編集

config/view.php

// compiledの部分を修正
'compiled' => storage_path(),

bootstrap/app.php

// 追加
$app->useStoragePath(env('APP_STORAGE', base_path() . '/storage'));

composer.json修正

gcp-buildを入れないとdevパッケージが入ってしまう

composer.json

"scripts": {
        "post-install-cmd": [
            "chmod -R 755 bootstrap\/cache",
            "php artisan cache:clear"
        ],
        "gcp-build": [
            "composer install --no-dev"
        ]
}

YOUR_APP_KEY変換

$ sed -i '' "s#YOUR_APP_KEY#$(php artisan key:generate --show --no-ansi)#" app.yaml

展開

$ gcloud app deploy -q