For a window that height my guess is lots larger. Theres mathematical formulas to work out how big is needed. Edit: No, sorry, that's for north.
For west the sun is going to shine in the window from when it reaches past the eaves until it sets behind the horizon or the house next door or something. I reckon you just about need to roof the whole yard to block it which kinda ruins the open airey look.
So do you think have a 1.5m eaves would make it look weird? The builder did mention that if I make the eaves larger, I would have to make my windows shorter by a bit. If not I would be able to look into the roof.