I dont know about your community but;
Have at look at your catastral plan as our one I recall stated the amount of the house and the amount of covered terraces seperately. Our friends apartment just had one figure for the superficie construdia incl the terraces.
Elementos de construccion Vivienda and Otros Usos
If you change that I think you should tell them via getting a building licence
Ask an architect or a glass curtain specialist as they must be asked all the time. I think even if you want to make it more usuable it wont be a fortune as the cost of the works will be quite low?