So you want to play the regeneration game?

The prospect of developing 1,200 acres of east London - Europe's largest brownfield site - has really whet architects' appetites.

EMPIRE-BUILDING COMPUTER games are known as "God games" in the States. As the 8 million Sim City players know, playing God begins with colonising a site. Flat or mountainous, inland or seaside, different areas give different degrees of difficulty. Then you position toxic waste dumps, power grids, roads, railways, airports, docks, cemeteries. You control the workforce and where they live, the green spaces, taxation, emergency services.

London's new mayor will have a chance to play Sim City for real, on 1,200 acres stretching across the Lea valley in east London, from Stratford to Thameside, opposite the Millennium Dome. It is Europe's largest "brown- field site". The borough of Newham awarded responsibility for the masterplan to a Barcelona-based architectural team, MBM, which won a competition called the Arc of Opportunity - a pretty accurate description of the layout of the winning scheme. How it is implemented and funded will be first on the agenda for the mayor.

Since the Government and the Urban Task Force, headed by Lord Rogers, defined brown-field development as the solution to the erosion of the countryside, escalating land values have made luxury developments the only viable option for this valuable land. Will poorer, more diverse communities be pushed out? If so, where will they go? Potentially, this east London development is a minefield for the new mayor, especially as MBM have planned for 18,000 one- and two-bedroom homes to comply with changing British demographics.

And, unlike Sim City, the site is not virgin territory to colonise. MBM inherited some horrors: decaying depots, haulage yards and wastelands that will have to be reclaimed and replanted. Pictures of herons, eels, squirrels and skylarks decorate the pages of a brochure on natural habitat. Yew trees in circles are to be planted on the meridian running through Newham from Greenwich.

Clean water is a priority: "excessive discharges" from the Abbey Mills sewers, which currently run straight into the river, will be purified. Areas such as Canning Town, Stratford, Three Mills and Lower Lea Thameside will have their pearly-queen cores developed in many different architectural styles. Streets are to be called "backbones"; an 80-hectare "wet square" with a fountain is planned for the area north of the Stratford station complex, to contain flood waters. A huge flyover at the heart of the riverfront site will be wiped out but the Blackwall Tunnel will remain. The river Lea, which meanders through the site, is to be enhanced by reclaiming waterways and slicing through a canal.

Zoom in tight on the aerial view and you see the reason for the expansion all along the river Lea: rail links. Chris Wilkinson's giant glass-and- steel ribcage of a rail terminus in Stratford has rail lines springing like arteries from its heart.

All four short-listed schemes - from Ove Arup, Pringle Richards Sharratt and Patel Taylor, as well as the winner from MBM - acknowledge the terminus's handsome presence in the landscape.

Ove Arup broke down an aerial view of the site into abstract cluster patterns, but the judges could not spot any continuity with the surrounding fabric.

Pringle Richards Sharratt's novel idea was to sheath the A13 in a glass tunnel so that birdsong could be heard above the traffic, a solution one of the judges, Ricky Burdett, described as "prophylactic" - masking a problem rather than solving it.

Patel Taylor's pastel watercolours of pastoral scenes were broken up by a rather obvious insertion of the Barcelona housing grid pattern along the river Lea. However, MBM already had experience of brown-field redevelopment, having built the Olympic Village at the Games at Barcelona in 1992 and in the process turned industrial wasteland into popular downtown housing.

Now the Architecture Foundation is taking its road show to Newham. On 16 April Tony Banks, the Minister for Sport and MP for East Ham, will open the show at the Stratford Picture House. Residents are invited to register their vote and use the road show beacon, a collection of BT payphones and videos, to gather and transmit ideas.

Lord Rogers says that, as architect of the Montevetro Thameside block of apartments, which has a pounds 4m price tag on a penthouse, he is only too aware of the dangers of unfettered market forces. "If you say to developers that they have to compete for a piece of land, then they have to get the maximum return for their money. Maximum return means luxury apartments. Luxury flats do not make a city on their own - you have to have a mix. You need regulations to make sure that you have social housing together with private housing. "

The leader of Southwark Council, Niall Duffy, is honest about the pressures. He has 50,000 council tenants. "It would be remiss of my officers not to tell me when there's a piece of land that's worth some money. And if this money were generated, I could refurbish upwards of 2,000 properties. Tough choices, but I've got those options."