Automatic Backup to Google Drive/External Hard Drive

I was wondering if it would be at all possible to have some sort of automatic backing up of my documents and such to Google Drive or an external hard drive.

Basically, it would be nice if I could save the file to my mac's documents folder and have that version of the file automatically be saved to my Google Drive without me having to copy/paste the file there, or re-save it there.

Thanks.