Framing Basement Entry Bulkhead

I live in a house that was built in the 40's. One side of the basement entry stairwell is the well-house. The two walls of the stairwell are approx 3-inches different in height at the house. Approx 6 feet out, the walls step down 10 inches and finally meet the sidewalk almost 12 feet from the house. Rather than excavate and build a new stairwell, I want to frame this in and install a set of diy "Bilco" doors. In western PA, I want to eliminate snow, leaves, etc. from accumulating in the stairwell.

My question is regarding what materials to use. A simple treated lumber frame and corrugated metal siding? some type of moisture resistant sheet good? Aesthetics is important, but secondary to function.

Any recommendations would be much appreciated!

Thanks

 

think we need a picture to understand the install!

Had a Bilco door several houses ago, loved it!