1. Storage. Lockers are frequently "sketched in" on the blueprints but are usually NOT the responsibility of the builder to order. Make sure you get them ordered 3-4 months before the facility opens.
2. Library storage. Shelves, rolling shelves, cabinets?
3. Stands and chairs. DO NOT let your district order stands from National Public Seating. Their chairs are meh to decent but the stands are absolutely awful. Also make sure they order RACKS for both stands and chairs.
4. Check the sound treatments in the band hall and practice spaces.
5. Uniform storage - will you have concert uniforms for your kids or do they provide their own dress?
6. How many different keys do you need to get in and out of your space?
7. what's the size on the doors going in and out of the band hall? Can you get a 32" timpani through (double doors with removable bars are a MUST).
8. Are there network drops and electric outlets in every practice room AND storage room?
9. Do you have a sink or access to one? Water fountain?
10. Carpet or tile or other? (YOU DO NOT WANT CARPET. It gets moldy, dirty, and will be cleaned once a year AT BEST. Tile, however, is harder on your instruments. If you can, go with rubber flooring like in your athletics facilities/weight room)
11. Risers - and storage for them?
12. Projection screen and electronics hookups, including speakers for stereo playback?
13. Is there an outlet in the center of the room, or do you need to have a 30' extension cord to plug in your metronome? Or do you have a remote digimet/bluetooth hookup to said stereo system to hook up your iPad/Surface Pro/phone/personal device?
14. Directors podium, stand, and if you want it, chair? Or two chairs if you have two direcctors?
15. How will traffic flow through the room? Can kids get to their "areas" without having to crawl over each other or your percussion sections? How much walk space is there?
16. How much room for growth did you build in?
17. Where will kids leave their backpacks?
18. Do you have a place to post objectives, word walls, other mandatory classroom anchor charts or other things that some new (or your current) admin will come up with or your district will mandate? You need a whiteboard for teaching, and a bulletin board for postings. What other display space is there?
19. Where will you put your old trophies?
20. Do you have designated work space for repairs/sorting music/etc outside of your office?
That's off the top of my head. If I think of more, I'll post again.