In my story I have a space ship, constructed in orbit around earth by an advanced artificial intelligence, large enough to be a generation ship. This ship was never designed to land on a planet. The construction of the ship (or ships, but we're focusing on just one for the story) uses up the majority of the earth's resources, and make a large part of the population rather unhappy.
Rebelling against the AI, the population not aligned to it, manage to take the ship and travel in search of a new planet. Finding this planet, they are forced to land the spaceship (not figured out how or why).
They are able to land the space ship, but not without it sustaining some damage. I intend that, generations later (100-500 years, I'm undecided) the ship forms a large part of a city (repurposing some of the onboard structures and systems) for the colonists.
However I want a point of tension in the story to be that this new city-ship was never designed to land or support its own weight and is slowly collapsing under its own weight.
At what size would a space ship be, using modern materials, that could still orbit a planet (without burning up, or being pulled apart from tidal forces), but when it lands it can only just support its own weight. I want that part to then mean any extra weight in the city-ship or damage tips it over the limit.
I'm happy to assume some hollow structure, but not entirely hollow (I.e. no Dyson spheres or O'Neill cylinders.).
I'm happy to expend some handwavium in how the ship landed (parachutes? artificial gravity?) or transformed into a 'city' etc, as this is not hard science, but still science based, so long as that doesn't interfere with the risk of it collapsing eventually..