That's awesome that the builder framed the window opening already. That's the brunt of the "nasty" work already done. I'm always hesitant to start cutting into my foundation wall :-)
When I was seriously researching the installation of an egress window in my old house, the issues I had to take into consideration were
making the external window well big enough, handling water properly and picking the style you'd like.
I've seen window wells done with pressure treated lumber, stone, and all sorts of inserts that would do well.
Google images has a ton of styles that you can check out: https://www.google.com/search?q=egre...w=1211&bih=751
Unfortunately, I don't have any models/types of actual windows on hand, and I'm a USA boy, so will defer to those with local/more experience.