Help me please to fill out this.. window fram?

[Flaffy]

I've tried multiple things but I don't know how to fill this frame out. Please halp me.

 

[radarhead]

Create an arch that fits the outer curve of the glass pane, then use the clipping tool to remove the outer curve of said arch.

 

[Pocket]

Also that's kind of a lot of polygons for such a small window. I know I'm usually the advocate for higher polycounts on curved brushwork, but I'm surprised you were able to get that many without shrinking it below the 1HU grid.