You can accomplish this with a non persistent entity and a datagrid with data source as microflow. Add this datagrid to whatever page you want to display notifications and use the microflow I uploaded to model share as the datasource. This allows for multiple notifications to be displayed to a user.
This microflow will give you a good idea on how to get this started. You will still need to figure out how to neatly display this on a page, as well as handling the case a user has multiple user roles.
I also recommend adding a boolean on the notification table to disable certain notifications.
Also if you want to only display one notification, use the microflow in a dataview (you will have to make the changes in the retrieve and the end event to only return a single object).