SFDSO in StLouis before — ideal. Now — worst nightmare.

Console centered facing choir.

I've found that when the console is at a 90 degree angle to the choir it is FAR more flexible; the organist can look directly at the conductor (on a riser at the 'back' of the console) OR the conductor-organist can be better seen by the choir while conducting with one hand and eyebrows. (Choir in semi-circle facing altar, adjusting their position to accommodate the physical location of the conductor.) It's also a lot easier for the organist to see the celebrant if the organ is at 90 degrees.

The choir risers (with seating or without) in a U shape to help blend, preferably between the organ cases or directly in front of them. Two tiers, possibly three.
Mobile organ console is a must, this makes it easier when serving as just accompanist with a separate director or when doing it all.
Extra floor space or enough room in the center of the choral risers for instruments is ideal.
A corner where timpani can be placed is excellent as well.

HATE risers.
The place I work now has 3 rows of "build-in riser" (i.e., 3 different levels of floor.) this may work for a large group, but in a small Schola where the conductor also sings, it's a mess: it's hard to keep one's eyes on the music, and if you look up to the top row, the head's tilted too much for good singing posture.

1) Flexibility is key. There is nothing worse than a loft with nothing but fixed risers too shallow to fit a chair and a music stand for a violinist/trombone/serpent player, or risers too deep to fit a choir that fills 6 rows into the four rows provided. This booklet from Wenger (the people who make conductors’ platforms, orchestra/choral chairs, etc.) has charts for recommended amount of space for different ensembles. https://www.wengercorp.com/Construct/docs/Wenger Planning Guide.pdf Movable platforms would be better to me than built-in levels.

2) (if operating in a less-than-perfect world) provision for an undelayed monitor speaker at the organ, to give you a direct link with a singer in front. In any good sound system nowadays, the speakers in a big room are programmed with increasing delay from the front of the room to the back, so that you don’t get the soupy sound that results from speakers in back firing before the natural sound of the person speaking has had time to travel from the front. But if you’re trying to do music from two ends of the building at once, you want an undelayed connection to the vocalist. That needs to be planned while the wiring conduits etc. are being designed.

3) Elevator if at all possible. For all the jokes about stairs being the Great Eliminator and a good Retirement Planner for older singers….someone infirm is going to need to get upstairs at some point, you’ll want to bring up music stands and 50 new Graduals, some wicked person after you may want to bring up profane instruments like timpani or harp…

4) Storage. As much as possible, dedicated to the music department. For stands and lights, extra chairs, etc. Everything you don’t want to have to drag upstairs on December 23 and drag down after midnight Mass.

Here is the new loft without the risers. We love it so much. There was a nice hardwood floor under the risers and carpet.

I think it's a zimbelstern.

Yes, it is a zimbelstern. It has not been incoorporated into the organ. It is Kentucky.....so I have a bit of a redneck set up.... Haha! It has a long extension cord and power strip. Just flip the switch on the power strip to get it to work, and remeber to turn it back off before releasing that chord. I bought it myself about two years ago because I really wanted to have one for Holy Week during the Glorias on Holy Thursday and Easter Vigil.

Here's a diagram of our choir loft's layout. Most of the singers wind up in front of the chambers, but it is nice to have the space between them.

The blank area behind the pews in their dips is excellent for orchestral musicians. LH side for strings, RH side for brass / timpani, with the cantor stand shifted out of the way. When we are using area mics for the choir (good to have the option -- and not always inadvisable with carpet still on the main floor and with a full church, although I prefer not to), those spaces are beyond the reach of the microphones, and so the instrumentalists and organ sing directly into the room, for the most part.

A picture would be great, thanks!

I had the pleasure of visiting there about six years ago and I was absolutely amazed at how beautiful the church is. I was amazed to see so much of it is made out of marble—a rarity these days! To say nothing of the stunning organ and that huge window.

Looks awfully much like the Co-Cathedral of the Sacred Heart in Houston.
I, like many here, have played dozens of organs in my lifetime. Of these, the Pasi at the co-cathedral is my favourite. (Oh)! What one would give for some serious colour about this vast utterly colourless sacred space.'

This gallery requires a director and an organist. In my opinion seating in the choir gallery should mirror that of the choir's rehearsal space (vice versa, actually). It is best that the organ console should be before the choir for good communication. Of course, if one has a tracker this is almost a necessity.

This gallery requires a director and an organist. In my opinion seating in the choir gallery should mirror that of the choir's rehearsal space (vice versa, actually).

Couldn't agree more. If it were up to me, and there was no issue with money, a movable console in the pit would be first priority—and it would be easy as the whole organ is already electrified—none of the divisions are purely tracker. Even following the director through the mirror is a new and frustrating experience for someone (me) that has only ever used consoles facing the director at some angle or another. A remote console by the cantor would also be useful, but much more of a luxury. The time delay for a nearly block-long nave greatly reduces the enjoyment of making music in the liturgy at cantor-only masses.

I think the concept of a rehearsal space that mirrors the main space is fantastic. I've never had that luxury, but I would imagine that it would be very advantageous.

It is hard conducting from the console if there are no risers. In the case of my loft, we also removed the worst looking carpet (which was a big part of the motivation for the change). I envision my church eventually updating the organ as the old Peterson relay is very limited and I would assume parts will be more and more difficult to come by. I've considered a digital hybrid organ so that if the pipe fall too flat, we can just use digital sounds. This was an issue I had at Christmas. The handbell choir played and the organ was so flat I had to jump to piano whoch was less flat... ['Tis the program we inhert when we accept the job offer.]