"That one sign there started everything," he said.
The remaining 20 houses in stage 2 will only be available when their sections have been shaped, he said.
"The first houses were sold off a plan. The next ones will be released when you can actually see the shape of the subdivision finished, so that people will know what they are buying."
Amon is the Manawatū-Whanganui representative for Platinum Homes, and the owner of DML Construction and two building-related businesses.
He bought 8ha of land at the end of Tirimoana Pl on the outskirts of St John's Hill. The first 2ha has already been developed, with 16 houses built.
In December last year Whanganui District Council changed the zoning of 50ha of land in Otamatea West from rural lifestyle to residential. Amon began stage 2 on the remaining 6ha after that - another 36 houses and sections.
The subdivision will have two roads and a public accessway to a planted reserve with a stormwater pond at the bottom of the slope. The reserve's vegetation will include the kinds of plants that would have grown there in the past, following advice from local iwi groups.
All the sections will be "elevated" to preserve their views, Amon said.
"The thing is, this is a spectacular piece of land. On a good day you can see the South Island and the North Island ranges, and agricultural land."
Contractors ID Loader and Goodman have earthmoving equipment at work on the hill slope. Bare earth is being sprayed with a grass seed/polymer mix to prevent windblown dust.
The cost of shaping sections, putting in roads, surveying, changing titles and adding water, sewerage, stormwater and electricity connections will be nearly $2 million.
The sections will vary in size from 800 square metres to 1300 and 5000 square metres, and be "sympathetic to the rural outlooks".
"They need to be very special, lovely homes," Amon said.
The first of the 16 houses sold was built using power from a generator, before there was electricity on site. It's being finished and is for a local farming family moving to town.
The others are being designed, with resource consents for another five awaited.
All will be Platinum Homes of three or more bedrooms, and some will be built by DML Construction.
"We will not necessarily have the resources to build all of them," Amon said.
"We will be looking to sub-contract select builders."
The houses will be on some of the 600 sections that will become available over the next little while, Whanganui mayor Hamish McDouall said. He pointed to other development happening, in Springvale's Magnolia Cres for example.
More will be needed, because Whanganui's population has grown to 47,300 over the last two years.
"Having more people in Whanganui is a good thing, but we have to remember that we want to sustainably grow and that we don't want to push some of our current residents to the margins," he said.
Modest dwellings will be needed too. McDouall said the council's housing strategy is pulling what levers it can to address the housing shortage - "about four levers out of 20".
Council is also talking to non-profit developers of social housing.
"Hopefully one of those will commit to Whanganui and we will be able to work on that profile of dwelling," McDouall said.