Standing high up on the cathedral roof, Justo Gallego Martinez can’t hear what I’m saying without crouching down and turning his head against the wind. He’s still unable to hear, so he gestures towards a rickety old ladder which leads up on to the roof, and I clamber up to find him in the same stooped position as before. Keeping low to the tiles, I cautiously edge my way over as he watches with mischievous amusement.

Clearly accustomed to greeting visitors, he shakes my hand with hospitable candour. It looks like the hand of any other 81 year old, but it’s as rough as sand paper and deeply callused by years of manual labour – they’re the kind of hands that would take a week to clean. I stand alongside him, and together we survey the view in silence.

There’s a courtyard below us, and next to it the inside of the crypt is just discernable behind an unfinished wall. Directly in front of us is the steel skeleton of the main cupola. At almost 40 metres high and flanked by 2 unfinished, minaret-like towers, it dwarfs the other 10 cupolas which adorn the periphery of the structure.

I rarely use the Spanish polite form 'usted', but it now seems like the only appropriate way to address the man who has singlehandedly constructed practically everything that stands before us.

He tells me that he modelled the main cupola on the Vatican, and that he intends to extend the minaret towers by a futher 30 metres. He’s built almost the entire cathedral using scavenged, donated or recycled material, and it’s for this reason that the majority of the structure is only partly finished. When he lacks the specific materials to do one job, he’ll start another with whatever else he has available; it’s the only way he can constantly keep building.

The parallels with Gaudí are clearly not lost on him, but when we talk about it he’s surprisingly scathing of his architectural style and is especially critical of the Sagrada Familia - "Las líneas rectas no valen - sólo me gustan las redondas" (Straight lines are useless.  I only like round ones)..." It’s impossible to tell if he’s just being provocative or if he actually means it.

Aesthetics aside, it’s difficult not to be impressed by the magnitude of the project. Thinking that he must have had at least a foundation to work from, I ask him how the land was when he started. He points at a nearby stretch of wasteland. "Like that," he says. "I’ve been building for the last 46 years."

The recipient of little formal education, Don Justo started work as a farmer. He later became a monk, but after a number of devout years contracted tuberculosis and was forced to leave the order. The Cathedral was born out of his promise to honour Nuestra Señora del Pilar (an advocation of Mary mother of Jesus) should she help him recover from the disease.

He’s never had any building plans, and when I enquire how he learnt about architecture and construction, he tells me it was by looking at pictures and experimenting on his own. Just like a talented dyslexic or autistic person, his unorthodox methods are often misinterpreted as the actions of someone either illiterate or ignorant.  I suspect criticism is something that he’s become well accustomed to and that playing on his provincial manner and occasionally cantankerous nature is part of his defence against it.

There’s already quite a few visitors walking around, but just then a coach party arrives. It occurs to me that after years of being the village madman, we must all seem a little less like people and more like the physical manifestations of his unfaltering faith. For a few years now, helpful gestures and kind words of support from strangers have been a daily occurrence for him.

Clearly, there’s something in the individual significance of his personal odyssey that people can empathise with. Behind the outpouring of support and international contributions including mosaics, stained glass windows and murals is their desire for him to succeed. Perhaps it’s also for this reason that the ayuntamiento have let him continue building despite the fact that he's never had any explicit planning permission.  In fact, their only intervention thus far has been to prohibit tourists from climbing the towers.

Just next to the Cathedral’s principal entrance, he maintains a notice board filled with press clippings from around the world. His notoriety is now such that he was recently asked but declined an opportunity to speak in New York. In his native Spain, it was the advert below which was first to publicise his story. It brought him nationwide attention and a reputed €30000.

It’s now siesta time, and together we climb down from the roof and into the cool shade of the nave. The last of the tourists are just leaving as we walk over to the collection box in front of the main entrance. Taking a key from his pocket, Don Justo unlocks the oversized padlock and scoops a few handfuls of loose change into his pocket.

At the time I thought nothing of it - I shook his hand and left - but in retrospect, I wish I’d asked if the donations had changed how he perceived his work. After years of struggling alone, I wondered if help was even something he desired. On some level at least, a man who sets out to singlehandedly build a cathedral is surely looking for adversity, so it seems somewhat paradoxical that what he actually finds is unconditional support.

Whether this contradiction was even significant is difficult to say. But definitely, beneath the piety, a certain artistic turmoil is just discernable within him. One of his key concerns is undoubtedly the widespread perception of the Cathedral. Even to the untrained eye the peculiar combination of building styles and the widespread use of concrete is somewhat jarring. For others, the concrete casts of the saints' heads, skewered on metal poles and mounted from the roof, are the unmistakable work of a madman.

Clearly, the indelible marks of eccentricity have made individuals and organisations wary of staking their reputations on such an association.  He has neither the support nor the blessing of the Catholic Church, and despite bringing much needed tourism to an otherwise unvisited village, the town hall have so far avoided becoming involved.

All this seems a little unfortunate because should history judge him kindly, they’ll doubtlessly all be fighting over his legacy.  Until then, it’s as likely that the Cathedral will be condemned as it will become a revered monument of national pride.