"Every structure has an Achilles' heel. Once it is solved, the rest of the work is easy," the 48-year-old told AFP.
He needed 90 helpers for one of his most recent works -- a life-sized Lego tram made up of a staggering 1.8 million pieces.
Together they put in around 6,800 hours to assemble Doczy's most ambitious project that is now on display in a bustling square in central Budapest.
The 11-metre-long (36 feet) Lego tram -- commissioned by Budapest's transport companies and its tourist office to "public transport and creativity" -- has attracted droves.
"We've never seen anything like this before," said Malaysian tourist Lucas Chang, 32, while dance coach Barbara Rajnai said children in her son's and daughter's kindergarten told them to check it out.
'Megastructures'
A professional Lego artist for more than 10 years, Doczy works more like an architect than a builder, relying on specialist software to draw up plans and only assembling bricks when he needs to test out a particular design.
"Initially, I do preliminary sketches much like a painter, stacking bricks on each other in a digital environment," he said.
"I set up the scale, identifying recognisable elements and proportioning the other parts relative to that."
For his intricate dioramas, such as his model of the Heroes' Square in Budapest, every piece has to imitate a specific detail.
In "megastructures" such as the tram, imperfections even as small as a tenth of a millimetre could stack up, leading to instability, he said.
"I always compare it to quantum mechanics and gravity: in a smaller scope matter behaves differently than on a grander scale," he said.
Thus blocks are glued together, an internal frame is added for extra support, and experts are consulted to ensure structural integrity.
Doczy also added some baseplates on its sides to allow people to place their own Lego bricks, which "has always appealed to me, because it allows anyone to express their creativity and transform the sculpture into a community piece".
Doczy was fascinated with Lego at an early age, assembling bricks with his older brother, though Western products were in short supply in then-communist Hungary.
"We begged the neighbour's kids to bring their sets too, so we could build bigger structures. We had ambitions even back then," Doczy recalled.
His childhood passion was reignited years later when his nephew became captivated by the colourful blocks.
When he looked at his brother, "our eyes lit up and we realised we should start building again," Doczy said.
Moving back to Hungary from Indonesia -- where he had been teaching diving -- he and his brother set up a business called "Brick Workshop" in 2013 to create Lego designs and organise activities for children and adults.
'Too valuable to throw'
In 2014, Doczy's Lego model of Budapest's iconic St. Stephen Basilica was featured at a Guinness World Record attempt, when volunteers constructed the world's highest Lego tower at the time in front of the basilica.
Three years later, he was officially recognised as a "Lego certified professional" (LCP) by the Danish company.
The coveted title -- currently held by around two dozen creators -- is awarded to talents who "create stunning, innovative designs that help push the boundaries of creativity and engineering," a Lego spokesperson told AFP.
The perks are being able to regularly consult with other LCPs and access Lego's sculpting software that allows Doczy to order "from the 14,000 different pieces in production", he said.
But for some projects, he has to scour the thriving second-hand market to search for pieces. Luckily for him, even bricks from the 1970s can be found there.
"As a diver, I've never seen Lego bricks pulled out of the sea," said Doczy, who divides his time between Budapest and the Spanish island of Mallorca. "They are just too valuable to be thrown away."
