Plasterboard on roof rafters. Is this okay?
There is nothing wrong with installing drywall on the rafters. You mentioned it's pretty dusty up there, keep in mind the that dust is coming from the soffit vents and will continue to do so after the drywall is installed. You don't want to block off the soffit vents. Not sure where you live but if it's in a hot climate, do yourself a favor and wait until October to do the work. Good luck.