Indoor paintball field?
Agree with the above. Heating and remediation costs would kill you. Abatement of ACM (asbestos containing materials), lead, PCBs... You probably don't want to get anywhere near it.
I recently did a project for a client to examine demolition options for an abandoned 800,000 sq. ft. building (former psych. hospital). In okay shape, good bones / structure, etc. Demo estimate came in at over a $23M TPC, mostly due to abatement. $23
MILLION. For demo alone. Granted this is a huge building but it should give you some sense of how costly this stuff can get. It's a shame too because a lot of these older buildings are pretty nice and built strong - certainly better than the junk today, but the abatement regulations absolutely drive costs through the roof and make it impractical to do much of anything with them (including demolish) so a lot of them just sit and rot, creating numerous other problems (squatters, blight, etc.)
The heating costs would be utterly brutal. My place is 3,200 sq. ft. on two floors and it's a struggle every year - and I run very lean / efficient and have done a pretty decent job insulating, identifying cold air infiltration points, pellet / renewable fuel, smart thermostats, yada-yada. I can't imagine how it would be to pay for tens of thousands of dollars of natural gas or bunker oil a year (if you can even legally run the heating plant - if it's steam, good luck - you might need a steam plant operator's license ($$$) which is another reason people / institutions have ditched those systems and sometimes the entire buildings just to get rid of paying that overhead (yes, I've personally seen replacement of an entire boiler plant just so a facility could eliminate two steam operator positions - they cost that much).