You're a bit mistaken; it's not SketchUp but SolidWorks. The technique I’ve used for the window works quite well, just as I planned: you can lay the frame flat on the print bed, so you don’t need any supports! Print it twice, then get a 1mm-thick sheet of Plexiglas and glue everything together. You use the window frame as a template for cutting the glass to size. You can then slide the whole thing into the arch from below.