How about the turn buttons they use to hold screens in window frames? And why are you wanting to use wood? They sell aluminum screen track and plastic corners in Lowes/Home Depot. Just straight cut with a hacksaw, stick the corners in and add fiberglass screen/spline. Easy and fast. That's what I used to make our screens. Make the frame slightly bigger than the opening so that the screen frame sits on the hatch frame and use the turn buttons to hold it tight to the hatch frame. The curve of the roof should be a big deal since the aluminum screen frame will flex a little and the turn buttons will hold it tight. Just make sure you get turn buttons sized for the thickness of your screen frame. Also easy to remove and clean.
Turn button (back spacer was trimmed so the button sits flush on the window frame)