Question:
Is it a problem for a shul to rent its parking lot to a church next door?
Answer:
We are not allowed to sell or rent things to a church or to a gentile if we know that it is going to be used in order to promote the worship of the avodah zara, and it is assisting the people to worship the avodah zara. Aside from this, the fact that you are a shul would make it worse. This is because it would be a chllul H-shem for a Jewish shul to promote to worship of the Catholics.
Sources:
Y:D 151-1.
