IT is regarded as an architectural treasure despite decades of dilapidation and years behind advertising hoardings.

But this weekend experts showcased 25 visions of what could be for the “forgotten” Egyptian Halls, by prolific Scots architect Alexander Greek Thomson.

While more than 100 of his works once stood within Scotland’s biggest city, one-third have since been razed.

And the organisation behind the move say losing this troubled building to decay would be as devastating to Scotland’s architectural landscape as last year’s Glasgow School of Art fire.

The world-renowned “Mack” building, by Charles Rennie Mackintosh, was destroyed by the blaze, which happened as restorations ordered after a 2014 fire neared completion. Situated in the same city, the 1870s-built Egyptian Halls are regarded as Thomson’s finest achievement and were widely celebrated at the time of construction, even inspiring copycat designs in the US.

Its brightly coloured interior played host to a bazaar where imported goods from around the world were offered to Scottish shoppers and where musical performances and exhibitions were held.

But the upper levels of the Union Street landmark – later home to offices, workshops, showrooms and even a Chinese restaurant – have been unoccupied for decades and water ingress has damaged original plaster features and concrete constructions.

While retail units at street level are occupied, massive advertisement hoardings have been in place for years and though planning permission has been granted on numerous occasions for conversion to a hotel, these have stalled due to a lack of public funding to support a commercial development.

Scaffolding was put in place in the 2000s to provide protection from falling masonry, but no major repairs have since occurred, despite measures undertaken by the owner such as the installation of a temporary felt roof to stop further rain damage.

Restoration, it is estimated, could now cost between £5 million and £15m.

Scott Abercrombie, vice-chair of The Alexander Thomson Society – the body behind the two-day showcase and competition that spawned it – says the Middle Eastern-inspired building is a “masterwork” that would be “impossible to replace”.

The National: Alexander Greek Thomson ... one of Glasgow’s two great architects along with Charles Rennie MackintoshAlexander Greek Thomson ... one of Glasgow’s two great architects along with Charles Rennie Mackintosh

The 32-year-old hopes the exhibition, which will be open at the New Glasgow Society on Argyle Street until 4pm today, will help find new uses for the category A listed building. Designs put forward by a host of creatives include those for a museum, art gallery and community centre, all of which are centred around the needs of the wider public.

Abercrombie told the Sunday National there is “no other comparison”to the Egyptian Halls but the Mack building. “It’s of national importance,” he said. “You find its columns replicated in New York and Milwaukee, the influence was wider than just Scotland.

“Thomson, along with Mackintosh, is one of the city’s two great architects. His work was held in massively high regard and the thing that set him apart is the decoration he used, the design he brought was not the way anyone else was working. His buildings are completely unique and this one is his triumph. “The problem that the Egyptian Halls has is having been shrouded in scaffolding, people forget the quality of that facade.

“Separating the people from it means the people forget what they have.”

The society is currently in talks with other arts bodies over the significance and potential of the site.

The building was threatened with demolition in 2011 following an impasse in funding discussions with Glasgow City Council. However, the Alexander Thomson Society hopes that the designs included in the Reimagining Egyptian Halls event will spark a conversation about what it could be.

“One of the primary reasons it has not been used is not through a lack of private and public interest.

“In the last 20 years, the options looked at were either a hotel or offices. It’s always been commercially driven, rather than something more public. In that time, the costs of restoration have gone up from around £2-3m and we have missed that window.

“The estimates now vary wildly, but they do make it harder, especially when there’s a need for profit.

“I’d like to see it made available for public usage, there is funding available for those things.

“There have been a lot of questions about whether it can be adapted.

“But we have 25 examples that show it certainly can be.

“That gives us ammunition to have conversations with authorities about what could be done.”