Casting a ledge/shelf in a basement window

[frihol85]

Hello,

We have an older house (1923) that we are currently renovating the basement in. The foundation is deep and made of stone. We only have one window and would like to cast a ledge/shelf according to the inspiration picture (picture 2). There is quite a significant slope at our window (see picture 1). I imagine it should be possible to set a "frame" for the ledges with rebar and cast to have a slightly smaller shelf closest to the window and a slightly deeper shelf around the middle of the slope. Any tips or thoughts? I assume you would first want to cast the lower ledge so that the smaller one has something to rest on after some curing time.
We are complete newbies and appreciate any tips

 

[Lilllen]

Personally, I think it was a stylish and clean look as it is now. The current appearance also lets in more light, and since it's the only window, it's a shame to reduce the light intake.