Hello, and welcome to Just Answer.
Regardless of who built the church, it is owned by whomever has legal title to it. This would be shown on a deed of trust for the property. Most likely the Catholic Church owns the land and building. Now, if your relative who built the church did so for pay, this changes things. If they did so as volunteers, then no. Were they paid for their work? Did they have a contract for being paid for their work? If they did, and they were never paid, they could have filed a lien on the property to ensure payment. However, this still doesn't mean they have any ownership interest in the property.
If you would like to share a bit more information about this with me, there may be more involved in the church's ownership than is first apparent. Otherwise, I hope this answers your question.
Well, since you have to get the bishop's permission, it seems the church does indeed own the property. I'm sorry to hear it may be closing. Perhaps you might go as a group and discuss the situation with him . . . asking what you all might be able to do to help keep your church open.
I wish you the best of luck with being able to keep your church open.
Thank you for trusting me with your question.