Ask HN: How tall should a giant mutant spider be to break my roof?

If a gentle mutant giant spider could be heavy enough to come by, sit down on the roof and, unfolding it's legs through the tiles, devastates the whole house, the question that remains for me is: how tall should it be?

According to Wikipedia, the heaviest spider in the world weighs 175 grams for up to 13cm body length (Goliath Birdeater). Let's say that the mass needed to break my wooden roof (we're in the countryside) should be around 15kg per square foot. Dumbly, the arachnid should be around 80 times bigger, or around 10 meters long.

That does look pretty big indeed on paper but what do you think? Should it be bigger?

Have an awesome evening otherwise fellows