Active job

Convert a dead space above a staircase to a loft

We would like to add a loft above the central staircase, its 1.4 meters by 2 m (2.8 m2) At this stage I would like the floor and boards as well as the ceiling underneath, After that we intend to install the floor covers and paint ourselves. The attached photo is from the internet however its very similar, Our job is easier as the stairs actually go the other way which lead to a bedroom , so basically its just rectangle we need.