This scenario can be done out of the box.
Create a new page type called "Notification". Give it 3 fields:
After you save it go to Pages and add an new Folder under the master page called "Notifications". Use a blank page for a template. On the template, add a new Contribution List webpart. Configure it so someone can add a new Notification.
On your master page template, find a place to put your notifications and add a repeater webpart in that place. In the repeater configure it to look in the /notifications node and look for the "notifications" page type you just created. Also add a transformation so it displays that notification. Assuming you will only have one active notification at a time, set the TOPN to 1.
This should get you want you're looking for. If you wanted to add some additional workflow to when someone submits a new notification, create a new workflow specific to the /notifications node and have it email the appropriate people when someone submits a new one.