Many years ago there was a guy in the Bronx, NY who was going to build a skeet range in an old movie theatre. That was possible because of the layout of a skeet field The problem he was having was the sound. Theatres are acoustically live and he couldn't figure out how to deaden the sound without spending a fortune. Also, would it be economically viable since he could opnly fit in a single field?
To open an indoor trap range you will need lots of money. The rules and regulations in place by the EPA require a very elaborate ventilation system to vent out the gun smoke and the lead dust. On top of that you would need to put in noise deadening materialto "reduce" the gun noise. This is the stuff you might have seen on comercials where the car is in a "special room" with what looks like egg cartons on the walls. This is an acusticaly "quiet" room to be able to detect noise from the car.
Some time ago I read an article about an indoor trap field somewhere in Texas I think. VERY costly to shootthere. Membeership fees were also very high.
But; if you got oil money or are rich the sky is the limit.