Donate to the Lead Adventure Forum to keep it alive!
I've worked the orher way around before myself...I simply glued lengthts of styrene strip onto eachother, but stepped, as if creating a very wide set of stairs. Once I reached the height of the window I was going for, I left the stack to dry thoroughly, then cut out/off the size of the window, and added the windowframe by glueing more styrene strip around the louvred rectangle.The advantage is that you can make multiples very easily, depending on the length of the styrene strips one uses for the louvres. I only needed 4 at the time, but this method works with larger amounts without issue...
For louvered shutters you could use electric cable ties cut to length, depending on the width you need, I bought some ties about 8mm width to do this but of course never got round to using them.
I have done it loads of time this way but just using thin cardboard usually cut from business cards