There are no such restrictions that I am aware of--as long as it is not a place where alcohol is served or haraam things are taking place. Open air ceremony is perfectly fine once we keep away from all vices, and people are not distracted from remembrance of Allah. This could be the case when people fail to observe their Prayer and become occupied with the celebrations at the time of salah.
Whether the marriage ceremony is done indoor or outdoor, we are not excused from establishing the remembrance of Allah. So I wish you a blessed marriage. And enjoy the celebration and never fail to remember Allah.