Chamfer the green edges by about 0.1 to sharpen those edges.
Create another box and position it at the base of the windshield frame you just made.
Now just like the windshield frame, draw a spline all the way round to the center and the extrude along it. Throw a symmetry modifier on it. And chamfer the edges to sharpen them.
The next thing to make is the rubber that lines the edges of the windshield. This is acheived the same way with a box that is extruded around the windshield. Create the box and extrude it around as shown by the blue geometry in the picture then throw a symmetry modifier on it to make the other side.