The following is the best summary of this passage: "Brutus asks if he has offended anyone, and they say no. He then asserts that he has not done anything to Caesar that the people would not do to him, and that Caesar’s triumphs have not been downplayed, nor have his crimes been exaggerated. As Antony enters with Caesar’s body, Brutus says that Antony had no part in killing Caesar, but will benefit from his death, just as all the people will. Finally, he says that he killed his best friend for the good of Rome, and he expects the people to do the same to him if Rome will benefit."
What makes it a good summary is that it brings out the main ideas of the text and restates them shortly and cleary:
Brutus has indeed not gone against the will of the people by murdering Caesar: "none have I offended;"
Brutus acknowledges the fact that he removed a ruler for the people and that he expects the same people to remove him as well if they deem it beneficial: "I have done no more to Caesar than you shall do to Brutus" and "I have the same dagger for myself, when it shall please my country to need my death;"
Brutus wants to be fair by alluding to both Caesar's exploits and his failures: "his glory not extenuated, ... nor his offences enforced;"
he also said that Antony was not guilty of Caesar's murder but that it is still advantageous for him: "though he had no hand in his death, shall receive the benefit of his dying;"
finally, Brutus believes that his deed was a sacrifice in the interest of Rome: "I slew my best lover for the good of Rome."
Top-Down is used to refer to a situation in which decisions are made by a few people in authority rather than by the people who are affected by the decisions
