The roof is publicly accessible as a sort of patio area. I don't know if it gets used for events or anything like that.
Because its elevated its a nice space to visit... unusual in a way, especially for London.
A bit of greenery would be welcomed too - or one can visit the linear park opposite the station, and if you sit close to the ventilation portal you can even hear the trains as they pass close by. As the portal has highish walls the trains cannot be seen.
I have a film from here and the roof can be seen at around the 3 minutes mark (mostly filmed in the winter and before the Embankment was rebuilt with bike lanes)
I am not sure why but their playback system treats this as a 3D film - which it isn't - you can click the gear symbol to change it to 2D but some of the text is lost.
A bit of greenery would be welcomed too - or one can visit the linear park opposite the station
There was going to be another linear park there, as the station roof was to have been the footing for Lumley's Folly - indeed, one of the many things that scuppered the project was the discovery that the roof would have needed strengthening.