The book of Matthew wasn't originally written in Greek, nor did Jesus speak Greek. We see from other places something that makes more sense, where Peter's real name, Aramaic "Kepha" is transliterated "Cephas". In its original language, Matthew 16:18 reads "You are Kepha and upon this Kepha I build my Church." Kepha means Rock. The Greek translators could not call Peter "petra" because that name is feminine, so instead they made his name Masculine, but something is lost in the translation.
Why did Jesus change Simon's name to Rock?Actually, Petros means "pebble."
Good argument. Some things to pick on though:
1) Whether Matthew was originally written in Hebrew or Greek is a matter of conjecture. The church fathers from the 3rd and 4th centuries couldn't agree on this point, so I find it doubtful that we know better than they.
2) If Jesus grew up in Egypt and Galilee, then He probably spoke Greek, as it was the more common language in both places. He undoubtedly spoke Aramaic as well, the Bible attesting to it with notes from the original authors in several places, and it also attests He was able to read Hebrew (though it was a dead language used only by scholars in His day and time).
3) My lexicon of Syriac (Jennings) indicates that the word used in this verse means "a stone, a piece of a (larger rock)." It also indicates that the Syriac word is (also) a feminine ending, so the problem of gender between the words remains in this language.
In short, all of the same issues remain, you've just changed the language we're arguing in/about.