Finally got around to modeling the ladder for the roof hatch.
This is a 72 degree climb angle and I figure that's a comfortable angle while keeping the length of the ladder to a minimum.
Detail of the hinge parts. The top step is incorporated into the fixed mounts and is slightly wider than the ladder rungs. I could have put the step lower and make it possible for the climber to get more than just the ball of his foot on the step, but that would have made the final step over the hatch opening a little too high. (It's 11" from the ceiling to the top of the opening.)
In the stowed position it fits flush against the ceiling and doesn't interfere with the front ceiling light.