Melbourne 's Eureka Tower is Australia 's tallest building with a roof and habatil floor .
If built , the building will be 388 metres ( 1,273 feet ) high ; surpassing the Gold Coast 's Q1 ( 323 m / 1,058 ft ) and Melbourne 's Eureka Tower ( 297 m / 975 ft and Australia 's tallest building too roof and habatil floor ) , and will therefore be the tallest building in the southern hemisphere .
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