Thanks. But if i were to choose curtain, what type of curtain should i choose? 
If i choose day and night curtain, there will not be much ventilation right (assuming curtain put down) and i open the window? 
If i choose roller curtain, i can still keep it half or 3/4 open to let wind come in. 
My bedroom is quite close to other  flats and i am thinking of the best ways of doing it as well as having some privacy. 
Anyone free to give your advise.