That sounds like a ridiculous waste of money that could be better spent on other things...

That aside, you will have a logistical nightmare ever getting practice time as I am sure football then soccer will get priority. How would both the football team and the band practice after school in it?

Secondly, do you really want to use it very often. Part of rehearsals outside are conditioning. Kids get used to being inside then get thrown out for that first football game and that could be a disaster.