My proposal is three-pronged: i) to replace the rectangular extension with a triangular one that will allow direct light into the ground floor again; ii) to make use of all the window openings; and iii) to retain the lay-out of the inside of the old house.
The roof is designed in such a way that the presently bricked up window at the back can be opened up again. Windows in the new extension are in keeping with the windows in the rest of the house, except the one at the far end which is full height one, allowing an uninterrupted from the raised floor at the front of the house towards the garden at the back.
The ground floor rooms are each between 15 and 20 m2. Other levels in the house are a cellar and two bedroom floors.
This house is an absolute charmer!