He estimates that structures up but still under construction could be about 3600sq m, compared with the average New Zealand house which is slightly more than 200sq m.
The footprint of the big U-shaped structure might be about 1200sq m alone, he said.
"Even as a single-level home, it's already huge. You put another level on that and it's ridiculous," Mr Porteous said.
Mr Abramov appeared on last year's Forbes rich list as the 21st richest man in Russia and the world's 124th richest man. He is 52 and married with three children.
The magazine said he got a start as head of a research lab before the old Soviet Union imploded and then made a fortune out of exporting metals and coal from the Urals and Siberia.
"After the 1998 Russian financial crisis, he bought up hobbled steel companies and coal mines on the cheap," Forbes said.
His Helena Bay Holdings got permission to build a 233m walkway with a 14m long, 3.6m wide floating pontoon along the untouched coastline of Otara Bay, at the northern end of Helena Bay about 1km off the main road, to give him better access to his fishing boat.
The billionaire, due to make twice-yearly visits, is allowed to dredge up to 200sq m of seabed on the northern side of the bay until 2015.
Mr Abramov has close business links to Roman Abramovich, who owns top English soccer club Chelsea. He also has close business ties to Mikhail Dmitrievitch Prokhorov, the Russian billionaire and owner of the American basketball team the New Jersey Nets.
On this side of the world, work on the Northland property gives Mr Abramov improved access from his home to a 17m recreational fishing boat in the previously undeveloped bay.
A Northland Regional Council official said the applicant for the Helena Bay job was Northland Coastal Developments.
Its Coatesville-based managing director is Chris Seel, who has control of all building work there.
Rival builders watching the job closely said much of the work was nearly finished, with concrete laid around rocks at the foreshore, foundations down some months ago and walls now rising. Some wanted to know how the builder won the contract and which trade depot supplied the materials.
"You won't see much from the air. It's designed to look that way but the pontoon and walkway are finished and the house is not far off," said one local.
The application to the Overseas Investment Office said Mr Abramov could have wealthy overseas guests staying at his lodge residence, rumoured to have taken as much steel to build as an office block.
This billionaire works through Abramov Family Trust which applied to build a high-quality residence/lodge and ancillary buildings to be used by the owner.
It might also "be made available on a commercial basis to wealthy domestic and international clientele", said the application.
"In addition to the construction of the residence/lodge, the Abramov Family Trust will improve the farming business by the conversion of the farming operation from stock fattening to stock breeding.
In addition, the Abramov Family Trust has committed to spend $250,000 to improve the quality of pasture, fencing, stockyards, troughs and service tracks.
"The Abramov Family Trust also intends to carry out a programme of environmental and historic preservation initiatives," the office said.
He first made moves in 2009 when Helena Bay Trustees got permission to buy 215ha of land at Helena Bay Farm, Russell Rd, in Hikurangi, Northland for $15.9 million.
ALEXANDER ABRAMOV
* Forbes estimate US$7.5b
* Ex-scientist
* Russian steel magnate
* Head of EvrazHolding
* Building at Helena Bay, south of Bay of Islands
* Links with owners of major US and UK sports teams.
