It’s Sunday night in Beijing, and a private lift sweeps me up to the 32nd-floor penthouse of Jianwai Soho tower: the family apartment of Zhang Xin and Pan Shiyi, China’s most visible and flamboyant property tycoons. When the door opens, I am led into a huge living room, with floor to ceiling windows and amazing Chinese art on white walls. I have met them before, in London, and they greet me warmly, Zhang, attractive and charismatic, dressed informally in black trousers and leather gilet, and Pan, who looks like a clever faun, with dark eyes that miss nothing behind black-rimmed spectacles.

They have invited me and a couple of friends for an informal dinner, and we sit down to delicious Chinese fare, while the conversation is peppered with financial jargon. No wonder. Jianwai is just one of several large-scale developments they have built in Beijing’s central business district (CBD), making them the largest developers of residential and commercial buildings in the city. Married since 1994, they started their company, SOHO China, in 1995, and took it public last year, raising US $1.9 billion (£950 million) on the Hong Kong stock exchange – a high point in a dizzying career which has seen them build a fortune in 12 years through fusing brilliant land deals, marketing genius and innovative architecture in a city where until recently everything was grey.

By contrast, their buildings are designed by renowned architects such as Japan’s Kengo Kuma, and make use of dramatic visual effects, either white or black, with splashes of colour in the interiors. Their business and personal lives have also been publicly intertwined, turning them into style icons and lending a fascination to the brand they represent. “They are the It-couple of China,” comments Sein Chew, an investment specialist from Hong Kong and New York. Pan has become famous through his blog on property and society at sina.com, which quickly surpassed 30 million hits.

Their current portfolio includes seven mixed-use developments: from New Town, their first project, which they started in 1995, on land no one wanted, to Chaoyangmen, due to complete in 2011. There is a residential development in Boao, on the emerging leisure destination of Hainan Island, and the extraordinary “Commune by the Great Wall”. Opened in 2002, it was mainland China’s first high-end luxury resort – a showcase of houses master-planned by Hong Kong architect Rocco Yim and designed by Asian architects, including Yung Ho Chang.

Boao and the Commune are managed by Kempinski Hotels, as Zhang, by her own admission, was not experienced in running resorts. “It didn’t really start as a business; it was a dream,” she says, a dream fuelled by her interest in architecture. Now, corporate giants such as Motorola, LVMH, Diageo and the Museum of Modern Art New York come for business weekends and brainstorming.

In the process, Zhang and Pan (the Chinese put surnames first), 43 and 44, have become symbols of the New China. Their success is underpinned by a deep knowledge of their customers – both the international corporate community and the rapidly increasing Chinese middle class, who are building their fortunes in the economic climate that emerged with the reforms of the Eighties and Nineties.

After all, before they became billionaires Zhang and Pan lived the life that SOHO China’s customers aspire to, young cosmopolitan types for whom the SOHO concept – “Small Office-Home Office” – was perfectly suited. The concept was inspired by the emergence of internet technology, the rise of small companies and the need for more live-work spaces. The company changed its strategy two years ago, from luxury housing developer to a focus on office and retail developments – in response to a government clampdown on the top-end housing market designed to control soaring prices.

Their own home, informal yet elegant, makes apparent that they have moved on to greater things. Zhang and Pan are frequent speakers at international conferences such as the World Economic Forum in Davos. Zhang, chief executive of SOHO China, of which Pan is chairman, was selected as one of the “Ten Women to Watch in Asia” by the Wall Street Journal. But they are still adjusting to the responsibility of running a publicly quoted company.

“I am exhausted,” Zhang tells me, every inch the chief executive in a Prada tweed suit and stiletto heels when I visit her in her office. “Since the IPO, we are on a different level. The projects are just flying through the doors. Everyone knows we have capital and a brand name and there are thousands of developers thirsty for cash.” She becomes visibly excited when talking about her latest project, Tiananmen South (Qianmen) – 360,000sq m of conservation and 201,831sq m of new buildings, in the largest hutong conservation zone in Beijing.

Hutongs are the low traditional houses that have disappeared rapidly in China’s construction boom, but now the government wants to breathe new life into the city’s cultural heritage. It turned to SOHO China for this project, and the company took it on once the government had relocated the people living there. Her description makes me melancholy, the sweeping away of old for new in the name of progress; she acknowledges it was painful to watch parts of old Beijing disappear. But only three years ago, there were dilapidated houses with severe fire hazards, and “20 families living on top of each other, shops with lots of yelling and screaming, and grandmothers sitting with their grandchildren”, Zhang says.

For the project Zhang employed leading international architects, from Herzog & de Meuron to David Adjaye. The main street will open in time for the Olympics, complete with a large Apple shop. The company is restoring old façades or working with photographs from the Thirties and Forties to re-create the authentic style. The irony of SOHO China being involved in conservation when it was part of the modernisation process is not lost on Zhang, but she is realistic: “On the whole, everyone is better off than they were ten years ago. When I am mandated to do a new building I do that. But I am equally proud to rebuild [old] Beijing.”

In her office, there are photographs of their sons, Sean, 9, and Luke, 8, who go to the international school and speak fluent English. At our dinner, it was Pan who put them to bed, while Zhang continued the conversation. And at SOHO China, Zhang’s office is lighter than Pan’s more modest one. They are not very social: “My kids are my priority,” she says. Their lives rotate around work, family and, increasingly, a search for spiritual values. She became a Baha’i two years ago; Pan is a Taoist who is “still exploring”, Zhang says. She is arguably the more worldly. Her parents were Chinese immigrants in Burma who returned to Beijing in the Fifties; they were translators at the Bureau of Foreign Languages, her mother translating Chou-Enlai and Deng Xiaoping “from Burmese to Chinese and vice versa”, says Zhang. Zhang herself worked her way up from a garment factory in Hong Kong and an assembly-line job at an electronics manufacturing plant to study economics at Sussex and Cambridge, and later work on Wall Street.

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