Hi Lisa,
If the church hall/fellowship room isn't available, what about a nearby park? Seems like the weather should be cooperative that time of year... and a lot of parks have pavillions or other sheltered areas where there'd be protection juuuuuuust in case the weather isn't cooperative. I know there are parks around here where pavillions can be reserved at no cost by calling the parks dept.
Just a back-up plan kind of thought for you.
Cheers!
Heather