With a 10 foot ceiling, it's going to be the light that is your limiting factor, not the plant heigth. The light can only penetrate so far, so we need to know what type of lighting you are using, before we can suggest a max heigth. But, even if you are using a 1000 watt HPS, you probably won't want to go much more than 4 feet tall, finished heigth. That would be about 24-30" in veg.