How thick should the walls be to use it in winter?

It depends what "use it in winter" means to you. Storing things is a different question from sitting in it for three hours with a laptop.

Rough guide

Storage through winter — 12mm shiplap is enough. It'll keep rain out and stay dry inside. Things will be cold, but cold is fine for tools and bikes.

Occasional winter use, an hour at a time — 28mm. A 28mm log cabin holds some warmth, feels substantial, and takes the edge off. With a small heater it's comfortable enough for a hobby room you dip into.

Regular winter use, hours at a time — 44mm or an insulated build. This is the point where wall thickness alone stops being the answer.

Thickness isn't insulation

This is the thing most people get wrong. Timber is a poor insulator compared with actual insulation material. A 44mm cabin is much better than a 28mm one, but it is not the same as an insulated building.

If you want a garden office you'll sit in on a January morning, look at insulated garden rooms — they're a different construction entirely, usually with insulation in the walls, floor and roof, and often double glazing. They cost considerably more and they're the right answer if year-round comfort is the point.

The things that actually make the difference

1. An insulated floor. Most heat is lost downwards into the base. An uninsulated floor makes everything else feel pointless.
2. Glazing. Single-glazed windows undo a lot of good wall. Toughened double glazing is worth asking about.
3. Draughts. A well-fitting door matters more than 16mm of extra wall.
4. Power. If you'll want a heater, plan the electrics before the building arrives, not after.

Don't over-buy

If you're honest that you'll use it from April to October, a 28mm cabin will serve you well and save you thousands. The number of insulated garden rooms sold to people who wanted a summerhouse is not small.

Tell us how you'll use it, month by month, and we'll tell you where the sensible line is for your budget.