I made a few changes to a summary you have already checked. I would like to know if everything is correct. Thank you.

1) Prince Prospero decides to shut himself with his friends in his castle, whic ias a big magnificent structure with strong walls and iron gates.
2) All its rooms have Gothic windows and the glass is the same colour as the ornaments except for the last one, which has scarlet red glass and black tapestries and carpet.
3) About five, six months later Prospero decides to have a masked ball in seven rooms of his castle.His friends only stop dancing when the pendulum, gigantic clock of ebony, is striking the hour.
4) At midnight, before te clock finished chiming the hour, a strange man in a grave-like costume and a death mask presents himself and scares everybody.
5) There is blood over is costume and face and all the guests are disgusted by him. The masked man walks to and fro among the dancers with slow, solemn movements. Nobody dares touch him because they are too scared.
6) Prince Prospero tries to stop the mask with his sword but he falls to the ground dead.
7) Some of his friends try to seize the red death but they find there is no body under the costume and the mask. One by one they all die and the clock chiming ends too.

Please isolate the changes you made. This is at least the 3rd or 4th time with this particular passage.