Bob gave us the following link in msg 176179 
https://www.wisconsinhistory.org/Records/Image/IM13658  

     And I may have missed this design in the books I quickly perused however - 
The roof hatches appear to be diamond tread overlay material, and the hefty beams to hold the open hatches could underscore that they are plate steel, however I cannot recall seeing these roof hatches prior, and the accompanying latches.  Wow can you imagine being in a hurry to open those, or worse yet pinch a finger when closing them. 
   Modeled by a foil overlay? 
    Can anyone provide a bit of enlightenment as to the design?                                                                                                    Thanks      Jim Dick - St. Paul, MN