Many men throughout Scripture preached in the open air.  We can point to such Old Testament men as Noah, Jeremiah, Ezekiel, Jonah, and Amos.  In the New Testament, we find examples of open-air preaching such as John the Baptist, our Lord Jesus Christ preached in the open air as well like in the Sermon on the Mount, for example.  In fact, open-air or street preaching is how the Gospel spread as we see with Paul, Peter, James, and Stephen to only name some.