Updated

By Julian Linden

MELBOURNE (Reuters) - The Australian Open is about to undergo a major facelift as part of a long-term agreement to keep the grand slam at its current site.

Work on the first stage of the A$363 million (US$336 million) redevelopment will begin in April and is expected to be finished in time for the 2015 championship.

The plans include increasing the seating capacity on the showcourts, building a roof over the Margaret Court Arena, a massive undercover courtyard for spectators and improving player and media facilities.

The two main courts at the Australian Open are already equipped with retractable roofs but the addition of a roof on the Margaret Court Arena is designed to help end the annual argument about the timing of the event.

The scheduling of the Australian Open has always been a sensitive issue because local organizers like to run it in January during school holidays to attract bigger crowds.

But players have been calling for the event to be moved back to February or March to avoid the scorching summer temperatures.

"The Australian Open is one of our great events and its popularity will continue to grow, with annual crowds of more than one million people forecast in the next 20 years," Victoria state sports minister James Merlino Merlino said on Tuesday.

The Australian Open had also been at the center of a tug of war between the country's two most populated states after New South Wales announced plans to poach the event from Victoria.

Although the tournament has been shared between Melbourne, Sydney, Adelaide, Brisbane, Perth and even New Zealand since it's inception in 1905, it has been played continually at Melbourne Park since 1988.

As part of the new deal to redevelop the site, Melbourne Park has been guaranteed it will remain as host at least until 2036.

"This is an historic day for tennis and the culmination of a lot of work by a lot of people," Tennis Australia President Geoff Pollard said.

"Full credit goes to the Victorian Government for its ongoing support, and its foresight in recognizing the future growth of tennis and the Australian Open."

(Editing by Alastair Himmer)