Reference Codes of Practice AS 1170.1 2002, AS/NZS 1576.1 & AS 1657.
Live loading for a stage is 7.5kPa - temp. or perm. structure. Table 3.1, C5 AS 1170.1.
If a marquee ets. is going to be fixed to it, I suggest you find out how the system is proposed to be fixed to the stage. Either the wind...