Countdown to the FA Cup final: Is Wembley the world's greatest stadium?

Leakage from a roof section which required 50 drenched fans to be reseated during Saturday's FA Trophy final at the new Wembley was but the latest in a sequence of setbacks for the stadium which no less of an architectural enthusiast than Wayne Rooney has already hailed as "the greatest on earth".

The Manchester United and England forward will have the opportunity to test that assessment at first hand on Saturday as his team take on Chelsea in an FA Cup final that will serve as the official opening of a new stadium that has endured four years of wrangling, delays and rising budgets. Meanwhile, the attitude of those who have created the visionary arena is essentially this: into every major project a little rain must fall; embrace the bigger picture.

When 90,000 spectators converge this weekend on the stadium whose signature roof arch is visible for 40 miles around they will be assembling in a structure that is the largest football stadium in the world - twice the size and four times as high as the old stadium - with the largest roof-covered capacity in the world. The arch itself, at 436ft long, is the largest single-span roof structure in the world.

The Guinness Book of Records may also be interested in the fact that the new Wembley will, for good or ill, be the most expensive stadium ever, given that total costs have risen to £798m.

The original Wembley - christened the Empire Stadium - was more swiftly and economically delivered after being commissioned in 1922 in order to host the 1924 British Empire Exhibition. The building was completed by Sir Robert McAlpine's company within just 300 days - in good time to host the 1923 FA Cup final. The total cost was £750,000 - big money in those days, but a figure which, by even the most extravagant means of reckoning inflation, corresponds to no more than a third of the latest figure.

But according to the overseers of this new project, Wembley National Stadium Limited, the level of expense for the new stadium has been governed by the fact that they are building "the best in the world". They add: "You only have one chance to rebuild Wembley stadium and it would have been a betrayal of England's sporting heritage had we compromised on the design."

It is this philosophy which has contributed to delays that have frustrated football followers since the last match was played at the old stadium on 7 October 2000.

Early last year, when the confident assertion that Wembley would be ready for the 2006 FA Cup final was beginning to look a tad previous in the light of setbacks such as the collapse of the under-stadium sewer system and the shifting of one of the roof girders, Sir Norman Foster, whose company collaborated on the design with HOK Sport, issued a cri de coeur.

"Would it be the end of the world if it wasn't completed in time for that?" asked the man who has overseen a series of projects including Stansted Airport, London's Swiss Re tower (The Gherkin) and the GLA building. "In the long term, this building is going to be around for many, many years. The challenge is to give spectators more space - 30 per cent more than in old Wembley - but to also get them to feel closer - physically and emotionally close - to the action."

For those who have lived with the idea of delivering a stadium that offers a new level of luxury for the sporting spectator, what will matter most come Saturday evening will be the quality of the experience for those present, as Angus Campbell, a partner in Foster and Partners, explained. The new stadium acoustics, for instance, have been designed using recordings from the old stadium in computer simulations.

"We discovered that a vertical section where the roof was connected to the bowl caused the sound in the old stadium to reverberate and echo," Campbell said. "We kept that configuration to maintain the 'cauldron effect' at Wembley.

"But we also discovered there was some problem sound in the old stadium created by the executive boxes introduced in 1984. They acted as a reflective surface and created a terrible echo. What we have done is to make all our glass surfaces slightly concave, like saucers. That means that sound will bounce off it in other directions, rather than being reflected straight back.

"The old vertical sections under the roof have been replicated, so the acoustic effect remains. But what spectators now have at the back of the seating bowl is a continuous glazed wall, which offers great views out over London and makes it look from a distance as if the roof is floating on air." What have not been replicated, but improved, are the views. "The original stadium was very shallow," Campbell said, "which meant you ended up looking between the heads of those in front of you. Now there are excellent sight lines everywhere.

"The seats themselves are bigger than those in the old Royal Box, with ample legroom. There will be space for people to walk past without disturbance."

Another key element of the Wembley experience, the pitch, has been at the centre of complex calculation. Most stadiums built now are on a north-south axis, which means that shadows fall evenly across the pitch, rather than making one playing half dark, which can make it very hard for spectators and television cameras to follow the action.

The original Wembley was built on an east-west axis, but avoided the latter problem because of its sheer width, given that there was a greyhound track around the playing area.

"The downside of that," Campbell said, "was that fans were far from the action, particularly at either end, and we wanted them to feel closer to what was going on. But we wanted to retain the possibility of having the pitch almost completely in sunshine."

Thus the new Wembley has retained the same orientation, but the arch-supported roof of four parts - three of which are moveable - can retract to allow the sun and the rain to fall directly on to the turf below.

"The arch has been set so it casts no shadow on the pitch, of which 95 per cent can receive sunlight," Campbell said. "And the ideal times are from three to five in the afternoon between mid-May and the end of July."

The roof will not close completely, but if it rains - once that faulty section has been dealt with - only the players should get wet. Keeping spectators dry is a necessary part of earning the Fifa five-star rating which Wembley must have in order to host future Champions League and - dare we say it - World Cup finals.

Inside the stadium the old, dark, dank concourses have been replaced by five levels of airy atriums containing cafes, bars, shops and restaurants.

"The arch is already a feature of London, like the London Eye, or Canary Wharf, and it is lit from inside at night," Campbell said. "When spectators are on their way to Wembley the atmosphere will be building, because it is always exciting when you can see your destination.

"They will then experience facilities so much better than any other stadium they have known. The amenities, the seats, the view, the atmosphere - it's just so much better than the original. And when they are seated in the bowl in the Wembley atmosphere and they look out on a pitch flooded with sunlight they will be saying to themselves, 'This is the perfect setting for a sporting event'."

It is an inspiring picture. Let's hope Saturday sees it in full colours.