The Shed File is as thick as a Manhattan phonebook. It includes pages from Farmers Weekly that go back to 1986 and ads for metal frames in the Farmers Guard-ian that are as recent as March. Some of the sheds look like the royal Wendy house on the Isle of Wight, most look like holding pens at Guantanamo Bay, and some look like miniature Glyndebournes, designed for country house opera and non-denomin-ational memorial services.

Field Notes scrawled in pencil include:

1. How severe are your winters? If very severe, you want a barn so you can close the cows in. Suffolk: a three-sided shelter will do.

2. Predators?

3. Three-sided shed. Make sure the shed faces in the opposite direction of the prevailing winds. Livestock don’t like wind.

4. Cows are herd animals. Make it big enough for all.

5. Know your land. Place shed on higher ground so water doesn’t drain into it.

Designs with exact dimensions are a file within the file. These include an ‘Adirondack shed’ with a generous overhang and an oak shed that could have come straight from the archives of Lutyens.
There is even a list that’s worthy of a Seamus Heaney poem: string, tent spikes, telegraph poles, posthole digger, hammer and nails, quick-dry concrete powder, tin. Gloves.

When the writer E. B. White moved to his farm in Maine, he discovered that 20% of his time was spent farming and 80% building and repairing stuff. He never mentioned a Shed File, but I bet he kept one. When he built a scow, he worked from a picture in The American Boy’s Handy Book, building it ‘after a pardonable delay of thirty years, which is the time it took me to assemble the nails and the boards and the skill and the leisure and the patience’. He was thankful that his desire was as strong after that interval as it was originally. I can honestly say the same.

With the help of Richard, a carpenter and fencer who doesn’t require my Shed File, and Julian, a stockman who knows what cows like, we began building the shed on Wednesday. Because Suffolk is known for its mild, dry climate, I’d decided a three-sided shelter would be both practical and eco-nomic. During the pardonable delay of 20 years, I’d had time to master the Field Notes. As soon as we staked it out (so that’s what the ‘string’ and tent spikes’ are for), I realised that this was not going to be like the barn in the film Witness. Still, it felt like an act of faith and somehow a suitable beginning to Advent: the creation of a humble shelter.

And on the third day, the snow began to fall. The wood pre-servative for my three-sided barn is called Northern Tundra, a pale grey paint from Sweden. As the wind blows across the fields straight from the tundra of severe winters, the name now feels like a prophecy.

Week two of Suffolk Tundra and the poles stick out of the snow like an amateur version of Stonehenge. The cows circle the abandoned exercise in installation art, presided over by the elderly cock pheasant who spends the shooting season in this field, using sheep and cows as the even-toed-ungulates version of a human shield against the seasonal insurgency. Work on the shelter has stopped and I don’t feel as faithful as Job when God asks him ‘Hast thou entered into the treasure of the snow?’.

And yet, Advent is a season of waiting and hope. I hope by the time you’ve read this, the shelter will be finished and the cows will be stretched out like mahogany boulders on their beds of sweet hay. (Straw, actually, but hay sounds nicer.) The long-awaited shed will look like an Advent calendar by Matthew Rice and I’ve planned a little ceremony to celebrate. We will sing In the Bleak Midwinter and Away in a Manger, before plugging the iPod into the speakers for Bob Dylan’s greatest hits, starting with Shelter from the Storm.