I have come up with an overall concept nutshell...finally.
Here's the deal. It is a Garden City. Literally. Instead of flowers you have different types of fancy buildings (flashy sky-scraper type ones) instead of Fruit and Veg you have practical buildings (Town halls, Fire Stations, Power Plants...hey that's given me an idea...a power...plant. Anyway) and instead of shrubs and boarder plants you have Trees and Parks.
Instead of bugs, and greenfly and garden pests, you have us. The Humans. Wrecking all your hard garden-work.
The project would be shot like any garden program you've seen on TV; Ground Force, The Chelsea Flower Show, Gardener's World, etc.
Instead of Alan Titchmarsh and co. you have 'The Giants'. The Giants now are washed up and old, think of them as the 50's generation being hit by the 60s, they don't quite know what to do any more because of the Baby Boom of the 40s - 60s. This has increased the Human problem.
So The Giants have sort of given up and retreated to their shed. Because you know all gardens have that old creaky shed where your Dad keeps 12 pairs of shears, 23 shovels, and an odd number of mouldy garden gloves. They keep to themselves and don't tend to their "Garden" any more.
This is until little Jez stumbles across them. He's been neglected by his ex-pinup-model Mother (Stage named 'Sticky' which is a play on Twiggy) who has grabbed the 60s with both thighs and is trying desperately to thrust herself back into the limelight.
Jez (age about 6-8) is curious, and very bright. He's a lot like Calvin from Calvin and Hobbes and sometimes uses surprisingly big words.
Jez is out exploring one day when he finds 'Big'. The Baby Giant (age 1-2) who has also wondered off exploring. The Giants find Big after a worried search and thus find Jez. Jez persists and follows them back to their shed to the Giants annoyance.
Through Jez and Big's inquisitive nature the Giants rediscover their love of gardening and vow to re-do their Garden and claim it back from the human 'pests'.
When the Giants reveal themselves to the Humans this is were 'Arky' comes into play. Until now most Humans had accepted the wonky buildings because they were all, 'doped up' (this would be shown as hippies etc going heymaannn coool rather than showing drug-taking). Arky though, being a nerd and intellectual avoided drugs and always knew something was up. He becomes fascinated by the Giants and befriends Jez. Through his relationship with Jez, he finds Sticky (Jez's Mother) and becomes her love interest because she starts to see that she's been a bad mother and neglected her son. She also falls for Arky because he doesn't take her at face value like everybody else.
The conclusion would be a happy ending where the humans and giants manage to live together in harmony. Much like Humans and Bees (which can be seen as annoying but are actually quite useful, as are most bugs). So the Humans help tend to the garden and they don't litter quite so much and they reduce their pollution.
I envision this parodying the start of environmental awareness at the start of the 70's were the theory of Global Warming really began to formulate after the economic boom of the 60s were commercialism really took off.
I was going to colour this but I quite like it how it is. It's the inside of the Shed. It has a bit of a 'Tardis' effect in that there is a remarkable amount of stuff for a Shed of this size. Even a Giant's Shed. 
The final character, not a very major role; Dolf Rickman the town (garden) mayor. My idea was to have him, being so small and physically diminished, become obsessed with the Giants in a Kaiser Wilhelm type way with the Potsdam Giants Regiments of Prussia. However he's becoming more of an after thought right now.
