Originally Posted by Atskodinski
Can you explain further the idea of filling in the slope of the window to be square? To me, that seems to mean using a board on either the inside or outside and using a concrete patching mix to bring it all up level. Am I even close on this?
Not sure, but by the pic, removing the slope is probably out. Either too much work, or based on the grass in the pic, would be too low? or both.
I suppose there are several ways to fill it in. My first thought is to secure a board to the inside wall, below the window, level with the high point of the slope. Then fill. What kind of concrete, how to prep, etc. is for someone wiser than myself.
If going with Rons suggestion, a store bought slider may be too deep. If so, that may work in your favor. You could trim the whole window out with the proper depth of wood, thus having a place for the window to sit at the bottom, and be secured on the sides.
Good luck with it!