Potsothy Sallapa props a ladder against the back wall of his natural-foods store in Kensington Market, climbs to the top rung, hoists himself onto the flat roof and takes a long look around. To anyone else, it is just a roof, an expanse of grey tar paper. He sees much more. He sees fragrant herbs, fresh lettuce leaves and rows of fat tomatoes.

Mr. Sallapa wants to build a greenhouse on his roof and he is praying city hall will let him. If the project succeeds, he hopes it will be a boon not just for the foodies of Kensington but for the whole city – an example of how people can grow their own food in the midst of the concrete jungle.

A much-loved Kensington fixture, just "Pots" to everyone in the market, Mr. Sallapa knows his vegetables. He grew up on a small farm in the Sri Lankan city of Jaffna. He used to haul its produce to market in a bullock cart, setting off before dawn so his pals wouldn't tease him. His grandmother told him: "You will never give birth to a child. Growing a vegetable is the closest you will come." He told her to get real. Now, he says, he can see what she meant.

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When trouble broke out between Tamils and Sinhalese, he came to Canada as a refugee. That was in 1986. A few months after, Mr. Sallapa asked a Kensington Market grocer if he needed any help. The grocer asked him if he had experience. Mr. Sallapa told him he had none, except for working on a farm. "You can start tomorrow," the grocer told him.

So began Mr. Sallapa's three decades amid the colourful market stalls of Kensington. He worked nine years for the grocer, learning the trade, then moved on to other spots. Eventually he helped set up 4Life Natural Foods. When the Zimmerman family shut its big discount store at 210 Augusta Ave. after decades in the market, Mr. Sallapa, 59, moved in, turning it into a beautiful, open space that sells everything from adzuki beans to acai fruit bars to spicy curry-lime kale chips.

But, all along, he really had his eyes on the roof, the biggest in the neighbourhood and the perfect place for his dream greenhouse. He had a small garden on the roof of his old shop, just a few rows of plastic buckets full of earth and growing things. What he has in mind now is much bigger.

He would put a deck up there, build Plexiglas walls and make a plastic roof that could come off in the summer. Inside, he would set up rows and rows of plant trays. Greens such as lettuce, spinach and kale would grow in the cold months, tomatoes, cucumbers and other vegetables in the warmer weather. Heat from the store below would help fend off frost in the enclosure.

He is eager, almost desperate, to get on with it. From his tall Victorian house on nearby Nassau Street, he gazes down at the roof longingly, imagining the greenhouse taking shape. To him, it must be as the prairies appeared to the homesteaders: virgin territory, ripe for cultivation.

His architect has approached the city to see if the plan fits with zoning rules. If it doesn't, Mr. Sallapa will rally his neighbours and fight for permission at the committee of adjustment. He can't imagine why anyone would object. "I'm not doing anything bad. I'm just growing food."

The way he sees it, more people should be putting greenhouses and gardens on the roof rather than relying on food trucked in from California, at great expense to their bank accounts and to the environment. Instead of staring at their screens, families would work together to make things grow. What child doesn't like seeing a sprout rise from the earth?

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If it all seems a little zucchini-pie-in-the-sky – cities will rely on the country for most of their food for a long time yet – it is hard to deny the appeal of Mr. Sallapa's project and hard to imagine why the city would turn him down. Kensington would rise as one, trowels in hand, to back him. He should get his little oasis on the roof.

Until he does, he has set up a miniature one in the big front window of his store, with bright grow lights to keep things going. Showing it off to a visitor, he plucks a tiny sprout from its plastic home and offers a taste. Cilantro. When everyone else in the store has gone home for the day, Mr. Sallapa tends the little plants and imagines what might one day grow on the roof above.