To save your projects on a cloud drive, Dropbox or Google Drive, for example, you simply have to choose as bibisco projects directory, a directory on your PC or Mac that is synchronized with Dropbox or Google Drive.
bibisco never connects to your cloud account to retrieve files (in fact, bibisco never asks you to enter your cloud account credentials) but always reads a local directory that must be kept synchronized by the cloud service.
you have to select a local directory (i.e. /Users/andreafeccomandi/Google Drive/gdrive-bibisco-projects) and not a network directory (i.e /run/user/1000/gvfs/google-drive:host=gmail.com,user=xxx.yyy/1lpNnSQwU6nKUpaVq21hxvvAKigncclO6)
You choose the bibisco projects directory when you first launch bibisco, and you can change it from the settings menu.