Hello again, I will take an extensive look at that, however even with fans, the hottest air will float to the roof... so the roof will still get to 140F or warmer.
A battery of ceiling fans mounted about 20 Inches below the roof will mitigate the problem down to perhaps 120F at the roof. At the very least you will need some high mounted fans.
Beyond that, roof insulation is an issue if the roof is not insulated very well you will most likely need many more heaters in the winter... in the summer a hot roof will actually help heat the building.
What most people do not realize is how the electric company charges for power, You end up paying more than the base rate, 10 cents per KW or whatever... there are *demand charges* and tiered pricing charges.... the utility company figures if they have to stand by to produce whatever your 15 minute peak usage is, that they have the right to charge you a 40 or 50% surcharge (there is legislation on that). Its a much bigger issue in total than you might realize, I can spend a few hours filling you in those details... the end result will be a decision your part most likely will be to make a special room with an 8 foot ceiling for the 100F exercises.... that is how it will likely shake out after you understand the scope of the situation.
Meantime tell me how many square feet in the building, what percentage is used for the 100F exercises, and what the winter outside air conditions are.... and what hours per day the 100F conditions are needed.
Beyond this 100F situation is *humidification... in summary its like this, if you heat 20F winter air to 100F the resulting humidity will be well under 5 or 10% (35% or higher is healthy) it will take very significant humidification take the entire building up to 35%.... these cost drop exponentially if you limit the 100F exercises to single room with an 8 foot ceiling.
Other options: Overhead gas fired infra red radiant heaters, these heat people, the furniture and the floor without having to heat the air so much...I am not so sure that this sort of heat will be viable for your application, but I am mentioning it so that we do not forget to consider it.
Here again in summary: Heat rises forcably.. it is displaced by cooler air at floor level, this is a serious consideration in the typical 70F heating design, it becomes a huge problem if you want to heat to 100F at floor level with a 20'+ roof over head.
Let me know about all of the above mentioned details please, we can go from there.