Two new public spaces will include a southern square modelled as a city piazza decked out with sculpture overlooking space for performance art.
The second external area will be a new garden to the west of the pyramid-shaped building and the landscape will be designed for families and children.
Tate director Nicholas Serota and architect Jacques Herzog, a partner of Swiss architecture practice Herzog & de Meuron, revealed the revised plans last week.
The new 11-storey design will include a perforated brick screen through which the building will glow at night.
The old scheme was said to look like stacked boxes, was not as eco-friendly as the new building and had less emphasis on landscape.
The new 21,000sq m building and landscape is due to be completed in 2012.
Funding for the new gallery has included £50m from the Government, £7m from the London Development Agency and £13m from the private sector.