It’s the sort of ultimate rich boy’s toy that will have oligarchs like Roman Abramovich drooling in envy and scrabbling in their pockets for their credit cards.

But it 's not simply size that will make this gigantic 325-foot long so-called ‘giga-yacht’ an object of lust for the world’s richest men.

Despite its faintly ludicrous name, the WallyIsland’s unique selling point is that it is fully customisable so that its wealthy owner can transform the huge upper deck into whatever takes their fancy.

The WallyIsland's giant upper deck can include a full garden and a pool area, as these computerised images show

Designed by the Monaco based luxury yacht contractors Wally the yacht's giant deck could include a large, deep swimming pool, a garden and even a full-size tennis court.

It sleeps up to 40 crew and 24 guests, not including the owner’s own extensive suites, or course.

Massive fuel tanks can hold three-quarters of a million litres of fuel, and it will hold two smaller yachts and other assorted watertoys on board.

It will also contain a 1,345 ft gaming room, a library, a cinema and a gymnasium, spa and sauna area.

It's huge upper deck swathed in greenery and with a covered pavilion to keep out of the sun

Although large at 325 feet, WallyIsland falls some way short of claiming the crown for the world’s biggest yacht.

In 2003, Paul Allen, co-founder of Microsoft, spent £100 million on the 416-foot 'Octopus', which at the time was the world's largest yacht.

His boat has a permanent crew of 60, including several former US Navy Seals for security.

It has two helicopters, a 10 man submarine and a remote controlled vehicle for exploring the ocean floor.

The yacht has from for a number of other smaller boats to take out on small excursions

Even Allen’s yacht pales looks positively underpowered when compared to the sailing vessel owned by the Sheikh of Dubai, which comes in at a cool 525 feet.

The brainchild of Wally's chief designer Luca Bassani, the WallyIsland's price has still yet to be set.

‘The price of WallyIsland will be very competitive because she has a 'commercial' look with no fairing or paint - the mega yacht resembles a tanker and the rough finish contributes to her unique appeal,’ says Monica Paolazzi, a spokesperson for Wally.

Big enough for 24 guests and 40 crew and with room for extensive suites the WallyIsland will be the ultimate rich boy's toy