GCSE physics

Moved to Physics.

Any material or structure has a maximum amount of load it can withstand before breaking. If a meteorite landed on a concrete roof then the concrete roof would be smashed to pieces.
If the structure were able to withstand that load, then it would provide an equal and opposite support force. But it can't, so it doesn't.
If you put an ant on a pile of straw or on a concrete roof, it would be supported either way as its weight is extremely tiny and so won't break the straw.

So then you might ask "So it's not true that every force results in an equal and opposite force?"

When something falls, if you disregard air resistance, then it's only gravity that's acting. But a falling pen exerts a gravitational force on the Earth just as the Earth exerts a gravitational force on the pen causing it to fall. So when something falls, the Earth actually moves a tiny tiny amount, which results in momentum being conserved.

So, regardless, every force causes an equal and opposing force.