The Catholic Church expressedly forbids Catholic ceremonies outside of the actual building, and since you wish to be married by a Catholic priest, you are out of luck.
Personally, I find such a rule to reek of traditional legalism. The belief is that God is within the Church building; hence, your marriage is in the presence of God. This had its origins in the Middle Ages. However, why would God not be present outside of the Church building? Regardless, I doubt the Catholic Church will be changing this stance anytime soon.
Melon
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"He had lived through an age when men and women with energy and ruthlessness but without much ability or persistence excelled. And even though most of them had gone under, their ignorance had confused Roy, making him wonder whether the things he had striven to learn, and thought of as 'culture,' were irrelevant. Everything was supposed to be the same: commercials, Beethoven's late quartets, pop records, shopfronts, Freud, multi-coloured hair. Greatness, comparison, value, depth: gone, gone, gone. Anything could give some pleasure; he saw that. But not everything provided the sustenance of a deeper understanding." - Hanif Kureishi, Love in a Blue Time