I was able to design a band hall at a previous school. Be sure to ask for outlets in the floor - super helpful to not have wires trailing across the floor.

Also, avoid having a perfectly rectangular band hall. One of the walls should be angled or offset to avoid standing sound waves in the room.

Be sure to have lots of instrument storage and room to add more if needed.

If you can, have trophy shelves installed on the walls to save storage space.

Hope this is helpful!