Hi Alejandro,
First of all you could refer to the logic explained here https://my.webratio.com/learn/learningobject/reusable-models-master-page-v-72 to model a part of layout common for pages inside the same Site View. Then you may have to create and customize a style project to apply required css rules to render the content of this part as you need.
For example you could model a Details Component to show info about the logged user into the Master Page and draw Flows starting from this Details to reach dedicated target Pages or Actions such as user profile, logout and so on. The related links could be rendered as list items and managed via css and via javascript to show the desired dropdown menu.