The problem is then you have two short ladders. You throw your two half ladders off the roof and they don't magically stand end-to-end for you. You have to cut with a twist to ensure the last rungs are entangled with each other so the half-ladders are hooked together. Then you can hang one off the other and reach the ground.
Each rung would go from a cylinder to a half-cylinder, but should still be rigidly connected to either side of the ladder all the same.