Normally, the clergy of the parish preside at the celebration of marriages in that parish. If you want another cleric to preside at your marriage, you must obtain the consent of the ecclesiastical authority of the parish — the rector, interim priest in charge, or church wardens.
Our Church discourages weddings outside of the physical church building because having a wedding in a church asserts the importance of the Christian community in the marriage, while having it outside tends to diminish the role of the Church and to dilute its rules and traditions.
If you do get married outside the church building, you need to bear in mind that canon law requires that your marriage be celebrated with the consent of the ecclesiastical authority of the parish (i.e. its rector, vicar, or priest-in-charge) within the boundaries of which it takes place, and recorded in that parish’s register (records).