least one preferably two roof sections 40 of a generally planar roof structure that substantially cover the opening 39 each roof section 40 is supported by at least one preferably two self supporting generally monolithic piers 42 a typical embodiment of each pier 42 is connected to the roof section 40 via a roof connecting part in the form of a roof support bracket 44 movably mounted on the pier 42 for displacement of the support bracket 44 and the roof section 40 relative to the pier 42 a typical embodiment of a roof deployment mechanism 46 better seen in fig1 connected to the support bracket 44 activates the displacement of the roof section 40 between a closed or deployed position in which the roof section 40 covers a respective portion of the opening 39 as shown in fig1 to 7 and an open or undeployed or retracted position in which the respective portion of the opening 39 is uncovered by the roof section 40 as shown in fig8 to 14 in the retracted position each roof section 40 is preferably completely overlaid by a portion of the fixed roof 34 but could also be located above the existing roof structure 34 or simply at least partially over an uncovered grandstand 45 schematically shown in dotted lines in fig8 or outside a stadium outer.