The problem of automatic design of acoustic spaces is prevalent in architecture and room acoustics. We present a novel algorithm to automatically compute the optimal materials of large architectural spaces. Our method uses discrete optimization techniques to determine the best material configuration for desired acoustic properties of a structure, while taking into account properties of real-world materials. An efficient acoustic wave solver is used to accurately compute the acoustic impulse responses that drive the optimization process. Our method is tested on various computer representations of real-world scenes where we show how new material characteristics can be computed to improve the scene's strength, clarity, and reverberation time.