The competition, purportedly run by the British Biological Architecture Foundation, was to design a castaway-type treehouse for beautiful remote beach areas in China, Vietnam, Hawaii and Fiji.
Spotting the competition late, he put in a 50-hour effort with a midnight to midnight stint on New Year's Day and managed to complete his entry six minutes before the January 1 deadline.
Several weeks on, however, time lost and potential damage to industry goodwill from what turned out to be a "bogus" competition has him angry.
Mr Roebuck, who owns architectural design company Structural Integrity, became suspicious when he received a request to pay the $US70 ($NZ88) entry fee to a large third-party payment website, instead of by invoice.
When he asked for office particulars and none were forthcoming, he decided to investigate further, finding a "crude faked website" claiming to be the foundation.
Mr Roebuck emailed the foundation, challenging its existence and threatening legal action, to which he received replies assuring of the foundation's existence.
He then tracked down David Greenburg, the original eco-architect and organiser of a previous legitimate treehouse competition, whose concept had been duplicated by the site.
"He was terribly sorry that I had been swindled and had been trying, along with National Geographic, to get the bogus site exposed," Mr Roebuck said.
Mr Greenburg runs an exclusive treehouse resort in Hawaii and is president of the Treehouses of Hawaii society. The competition had claimed National Geographic would document the build.
While Mr Roebuck avoided losing his entry fee, he estimated the amount of chargeable time he invested in the project to be worth nearly $6550.
"I value the time spent making something creative, but it's time when I could have been doing other projects or been with the family and I can't get that back," he said.
Mr Roebuck said his own online inquiries indicated the culprit was based in Cyprus.
While the New Zealand police told him it was "out of their hands", he said he was still pursuing other options, together with parties that had their identities used in the scam.
Charging a small entry fee was not uncommon, but he said he probably would have caught on earlier had he not been in such a hurry to get his entry finished by January 1.
He won the Formica Formations Design Competition last year with his "Beehive" chair, and had previous success designing a modern church with late Invercargill architect Neil McDowell.
