Finish walls/ceiling/shelf of a 4x4x12 ft cupboard - Plastering job in Edinburgh, Midlothian

Job description

This tall cupboard was clearly a work in progress when I bought the flat. It has two built in shelves, is partially finished in plasterboard, but is mostly very rough plaster. I don't care what the final surface is - it could even be paper - but the main job is actually creating walls that can be decorated. I will need some advice as to the best approach, but I am ready to proceed with the work in March.