Open Automator
Create a new Application
In your Google Drive, create a folder called Backup
In the Backup folder, create a folder Desktop, Documents, etc for each folder you want to back up.
Create these processes:
Get Specified Finder Items
(choose all the folders in the Backup folder - not the Backup folder itself)
Move Folder Items to Trash
Get Specified Finder Items
(choose Documents)
Get Folder Contents
Copy Finder Items
(copy to the Documents backup folder location and choose replace existing files)
Get Specified Finder Items
(choose Desktop and click options and choose Ignore this action's input)
Get Folder Contents
Copy Finder Items
(copy to the Desktop backup folder location and choose replace existing files)
Repeat these steps for each folder you want to back up
Get Specified Finder Items
(choose FolderToBackup and click options and choose Ignore this action's input)
Get Folder Contents
Copy Finder Items
(copy to the FolderToBackup backup folder location and choose replace existing files)
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Save the Automator application to the Applications folder
Go to System Preferences -> Users & Groups
Click Login Items
Add the application you created in Login Items