ok, well, the gaps at the sides will be closed by masonry (another 6" thick of granite goes outside the block there now), the top will be covered by a steel plate.
But, I made the shutters close at an angle oblique angle to the walls, because, if some vandal types decide to shoot at the building, they'll tend to shoot straight at it. So, any bullet impact, will not hit square, but at an acute angle, related to firing position. It gives an effective thickness to the the shutter of about 6", and because of the angle, most bullets will ricochet anyway, hitting the building walls, where no damage will occur. If, they shoot perpendicular to the shutter, and if the bullets at some point penetrate, they'll not be in line with the windows behind, and so, less chance of breaking them, or people ensconced within.
Yeah, Elorrum, the shutters can open to form the cross/slit for firing, or close tight, from inside, you can set the gap as needed.
And, I'm sure this would not have been in a castle book, in that I (think) I thought of it myself, relating to bullets and drunken hunters/kids, sitting somewhere saying "I bet you can't hit that building, Clem".........
for indirect lighting, if all shutters are closed, I have a 3/4" thick tempered glass top, horzontal, on top of the Gregorian looking roof center/cap, and below the Runes, which are held above on steel bars. It shines down trough a venting system, lined with copper, to make the light reflect and such, and just look cool.