It's done all the time apparently....
http://sanfrancisco.cbslocal.com/2014/04/17/san-francisco-49ers-new-levis-stadium-designed-to-rival-seahawks-stadium-for-crowd-noise-super-bowl-l-santa-clara-acoustic-guiness-record-12th-man/
"the new generation of stadiums now incorporate design features that help boost fan support by trapping and amplifying crowd noise. The most important aspects are to keep the size of the stadium as small as possible, and to provide reflecting surfaces that can turn the noise back to the crowd....The San Francisco 49ers’ new Levi’s Stadium, in Santa Clara, Calif., has been designed with this in mind. It’s small, and fits snugly into its dense urban location. One of the long sides of the oval has been truncated, with the media booths placed in a tower that reduces the footprint of the stadium and will help reflect sound back towards the fans....At the Seattle Seahawks’ CenturyLink Stadium the large overhanging roof reflects noise down towards the stands.