David Pinto points out an interesting article about rules for opening and closing roofs in Major League stadiums. The decision for the position of the roof at the start of the game rests with the home club. Once the game starts, however, the umpire crew chief has final say as to whether it's moved. The roof can only be moved once per game. If it starts open, you can close it, but then you can't reopen it and if it starts closed you can open it but not re-close it. Same goes for the wall panels in the outfield.