You'll find constructing flyscreen for this type of window slightly more difficult than a standard window. You'll need to work around the winding mechanism as the bottom ledge is not flat due to its position. If you were to fit a standard screen there will be a gap on either side of the winding mechanism. At my property, someone has pop-rivetted a Metal Mate 20 x 12 x 1.4mm 1m Aluminium Unequal Angle to the bottom of the screen and cut out around the winder to fill the gap. I've included an illustration below of how that would work.
Alternatively, you could create a flyscreen frame that fits around the winding mechanism. You would need additional corner pieces to do the returns around the winder. I haven't personally seen this done before, but I believe it would be possible.