Rem Koolhaas cuts a striking figure as he strides out in search of inspiration. Roaming the grounds of Gartnavel Hospital in Glasgow's west end, the renowned Dutch architect, dressed in black Prada, is checking out the three sites he's been offered on which to build his first-ever Maggie's Centre.

Every so often, he stops to cluster with members of his party as they rush to catch up. This select group comprises Koolhaas's main collaborators on the project: Lily Jencks, daughter of Maggie and Charles, and Richard Hollington, an associate at the Office for Metropolitan Architecture (OMA), Koolhaas's practice in Rotterdam, which also has offices in New York and Beijing. Maggie's vice-chair, Marsha Blakenham, and CEO Laura Lee are also here from London, as are John Stuart and Steve Russell of NHS Greater Glasgow & Clyde - which has generously donated the space for the new cancer caring centre.

Being in the company of this superstar architect at the very moment of creation is a special experience - all the more so because there is absolutely nothing to see. There is no eureka moment, just a gentle nod or a discreet dismissal as he moves purposefully over the undulating ground. At each location he checks the outlook, the light, the wind direction, and the vegetation, or lack of it. Everything is in abstract; this is an exercise in information intake. You can almost hear his creative mind humming with possibility.

Koolhaas is responsible for some of the world's largest and most iconic modern buildings, such as the gravity-defying China Central Television HQ in Beijing which, when it is completed next year will be one of the largest structures ever made. Its two 800m-high towers are poised at an angle of 10 degrees and will be joined to form a continuous upward loop. His previous works include the jagged glass and steel Seattle Central Library in Washington, the Casa da Musica in Porto and the Dutch Embassy in Berlin. He is also working on masterplans for the new city in Dubai, which will be home to 1.5m people, and on the masterplan for the redevelopment of Bovisa, in Milan. The 64-year-old Dutchman co-founded the Office for Metropolitan Architecture in Rotterdam, where Zaha Hadid was one of his students. He won the Pritzker Prize - architecture's Pulitzer - in 2000.

Like Frank Gehry and Zaha Hadid before him, Koolhaas has a relatively minuscule 300 square metres at his disposal for this, the eighth Maggie's project in Scotland. You might expect the size to be a challenge for someone more used to large-scale commissions, but Koolhaas is delighted. "We're getting asked to do small things less and less," he says as he takes a short break. "I like the domestic scale of this. This is one commission we accepted with eagerness."

One of his early buildings was the 1998 Maison a Bordeaux, a home designed to accommodate a wheelchair-using private client, which he has described as "a series of caverns carved out from the hill for the most intimate life of the family".

Even so, designing a Maggie's is new territory. "This is a world we've never entered either in the UK or the rest of the world," he says. "I don't think it should be a building that challenges people to live better; rather it should have a direct effect on the people who use it." Koolhaas has been a friend of Maggie and Charles Jencks for 40 years, after meeting Maggie when they were both students. "I have never met anybody so delicate, vivacious and smart at the same time," is how he describes Maggie.

The Gartnavel Maggie's means Glasgow could be the first city in the UK to have a Koolhaas building - if it is built before his new HQ for the Rothschild bank in London, which has already been granted planning permission. It will also make Glasgow the only city in the world to have two Maggie's centres. The first was a conversion of the coachhouse at the Western infirmary, designed by David Page of Page and Park and opened in 2002. Koolhaas is in the rather more enviable position of being able to design the new Maggie's from scratch, but he is not one of those architects who eschews the past.

This is not his first visit to Glasgow. He was here 40 years ago in 1968 as a student at the Architectural Association in London to view the work of Charles Rennie Mackintosh. "I was not enamoured with Britain, because it seemed very gloomy," he says. "Scotland, by contrast, seemed impressive and monumental and very different from England."

He believes Scotland's tenements and, especially, its tower blocks were "very impressive and well done". More of them, he says, should have been preserved. "We cheer when the high flats get demolished, but soon nobody will remember anything from the 1960s and 1970s," he says. "We should remember that preservation is not punishment. There should be examples of everything we've built so that we have prototypes of good and bad. I'm constantly finding that the best things disappear."

As it happens, the site Koolhaas eventually plumps for is a sliver of space embraced on one side by the front of the old Gartnavel Royal hospital, an iconic Victorian building built in 1843 as Glasgow's lunatic asylum, and on the other by a bank of well-established tall silver birch, sycamore and lime trees. Beyond these is the main entrance of the new Beatson cancer hospital. It's the most elevated of the three on offer. "This is great because it is linked to the existing hospital, but far enough away from it for us to create another world away from it all," he says. "It has both privacy and a central position, both sheltered and slightly exposed."

It is tempting to assume his new building will be a modernist glass-and-steel affair, but Koolhaas will not be drawn.

"Our projects in Beijing and in Glasgow could not be more different, and I don't think I have a trademark style," he explains. "Here, I'm trying to imagine how we differ when we're sick from when we're well to create a space that will welcome and protect." He emphasises that he will take into account the "body of work" that already exists with the Maggie's Centres. "We want to be part of that."

And then it's off back to Rotterdam to discuss his ideas with Richard, the project team leader. They give themselves just a week to put together a concept design "because I like to create a bit of a creative buzz", he jokes.

Scroll forward two months, and Richard has just presented the concept design to Marsha Blakenham and Laura Lee in London. Speaking exclusively to The Herald, he says: "Our initial design is single-storey with a landscaped internal courtyard, which we hope will be planted by Lily Jencks. We have been looking at ways to address the light. It is a very intimate space where the natural light coming through the trees is dappled and very gentle. It will have a holistic feel that hopefully will provide respite and comfort for people."

It is too early to reveal any further design details, but Richard explains that at OMA they have looked at the existing Maggie's centres and the way they have been designed. "We've done a sort of evaluation of what works and what doesn't work and taken on board the opportunity to do something different," he says. "We're very happy with it. It achieves what we want it to, and in addition it is a very beautiful building."

Laura Lee, chief executive of Maggie's, said that getting her first glimpse of Koolhaas's new Maggie's was "very exciting".

"We were all bowled over by his ideas, which really complement the site at Gartnavel and the ethos of Maggie's. We are so lucky to have him designing this building for us. It will be a truly uplifting and comforting place for people affected by cancer."

A second design meeting will take place in London in September, and thereafter the planning process will begin in earnest. For everyone concerned, this project has extra potency. Koolhaas says: "I'm only ever planning to do one Maggie's."

cate.devine@theherald.co.uk