When we purchased the house there was a opening left in the drywall above the sink but no window or frame was installed.
Our house is unique in that the outside walls are 12" thick. This required me to use 2 x 12s to frame the window frame. The nice thing is that the bottom of the frame sits on the horizontal "C" frame. The "C" frame sits with the opening of the "C" pointing up. Placing the bottom of the frame on this meant that it is very sturdy. The top of the window frame is attached to the upper "C" channel. The space between the "C" channels restricted the height of the window to 3 feet. The width of the window ended up being 4 feet.
We decided on a casement window that cranks out. This makes the window easy to open reaching over the sink. Also rain doesn't tend to come in which makes it nice during the monsoon season as it will be raining but the temperatures will be quite warm.
Now it is time to close up the walls.