help on achieving a 40 db insulation

[josesalazar]

the idea is to insulate an ex church turned into a cultural center.
we mean to make it suitable for concerts, classroom, exposition center
and library
we are in need of a 40db insulation from the exterior at all frecuencies, i inderstand that that comes along with an excelent weather insulation
the space is a enclosed tenis court sort of
it's made ob brick walls up to the 2,4 meters high, then the whole structure, walls up to six meters high and the roof are made of metal. there's no insulation here wich means a lot of echoes, and being exposed to extreme weather conditions.
the dimentions are
length: 35 mts
width: 20 mts
height 8 mts
roof has an "A" shape at 20 degree angle. it splits along the center
comments and a lot of advice here although the idea is to keep costs low
thanks in advance for the advices