The surround around the new bedroom window is going to have a curved sill & head to match the original window. The original was likely a bowed double hung window, complete with curved glass! Unfortunately the existing wood was completely rotted, so time to start over!
We used pressure treated wood so it will last in direct contact with masonry. Here I am laying out the shape using a full size print of the new window details.
All laid out and ready to be cut with a jigsaw from the West Philly Tool Library.
For an extra level of protection and for ease of painting the window in the future we primed the wood using an oil based paint.