What is the zombie movie where people are trapped on roof?

You're likely thinking of "Night of the Living Dead" (1968).

This classic zombie film features a group of survivors taking refuge in a farmhouse, with one of the final scenes taking place on the roof as they desperately try to escape the relentless horde of zombies.

While there are other zombie movies with rooftop scenes, "Night of the Living Dead" is the most iconic example.