Internal Fire Exit

Hi everyone, On the top floor of our 3-story brownstone, we have a “fire exit” through a glass “escape window” on the roof. It is located in a chase at the top of the stairs from the parlor floor to the top floor – the traditional set up. I need to get a new ladder because the existing ladder is too short for my liking. Does anyone know if there are any required specs (height and weight bearing capacity, installation requirements, etc.) and where such a ladder can be purchased? I found a couple of seemingly decent extension ladders at Home Depot that could be set up permanently there – for example: 8.5′ ladder (carries 225 lbs), a 10.5′ ladder (carries 225 lbs) and a 12.5′ ladder (carries 300 lbs). Is there any chance that these could work? Many thanks, in advance, for your support!