We use zinc for bass pipes - lead is just too heavy. Wooden pipes are usually smaller and produce mellow woodwind sounds. It depends on what you want. The leathers are used in various inner workings of the organ. As the organ is being built, the congregation also needs to check to see if changes are needed in the sanctuary's acoustics and if any part of the sanctuary needs to be reinforced to carry the heavy load.
Acoustical tile is very bad for a church.
A hard surface that reflects the sound is best. Plaster and thick wall board, for example. Carpets aren't good either. Pipes 9 feet high weigh around 100 pounds. That's a lot of weight in front of the organ.