If you've spent any time researching garden rooms or garden offices, you've probably noticed something confusing very quickly: the prices you see online vary massively.
One site suggests you can build a garden office for a few thousand pounds. Another quotes figures that rival a small house extension.
When I first started looking into building a garden room office myself, I ran straight into this problem. On paper, it all looked affordable. In reality, once I actually priced the materials properly, the numbers were very different.
This post is about closing that gap.
I'll walk through:
- The real costs involved in building an outbuilding today
- How DIY builds compare to ready-made garden rooms and log cabin kits
- Why so much online pricing is misleading or outdated
- How changes in timber prices over the last decade affect your budget
- One often overlooked cost that applies to almost every build: electrics
The moment the numbers stopped making sense
When I started researching garden rooms, I did what most people do: read forum posts, watched YouTube builds, bookmarked a dozen "How much does a garden office cost?" articles.
A lot of people were talking about building decent-sized garden offices for surprisingly low amounts. At first glance, it felt achievable.
But then I sat down and actually started pricing it properly — timber, boards, insulation, roofing, fixings — and the total was nowhere near what I'd been expecting.
That disconnect wasn't because I was doing something unusual. It came down to two very common issues that affect almost everyone planning a build today.
Reason #1: Most real-world build costs online are out of date
One thing became clear very quickly: a lot of the cost examples people rely on are old.
Many forum posts and blog comments discussing "my complete garden office cost" are:
- 5, 7, sometimes 10+ years old
- Based on very different material prices
- Written before recent volatility in timber, boards, insulation, and roofing materials
They're still useful for understanding process and design ideas, but they're a poor guide for modern budgeting.
Timber is the biggest culprit here. Over the last decade, UK timber prices have risen significantly and have also become far more volatile year-to-year. Even ignoring short-term spikes, the long-term trend is upwards.
What that means in practical terms is simple: a timber frame that cost £X to build in 2015 will almost certainly cost substantially more today. The same applies to sheet materials, roofing systems, and fixings that scale with timber usage.
Unfortunately, those older builds are still ranking highly in search results and still being referenced in forums — so they quietly set expectations that no longer reflect reality.
Reason #2: Headline kit prices are not finished-build prices
The second surprise came when I started looking seriously at self-build kits and log cabins.
At first glance, kits look like an excellent deal. And to be fair, many of them are — for what they include.
The problem is that most kit pricing you see online is for the base kit only.
Key elements that turn a structure into a usable, year-round office are often listed as "upgrades", including:
- Insulation
- Thicker or higher-grade structural timber
- Proper roof systems (such as EPDM instead of basic felt)
- Vapour control layers
- Internal linings
- Upgraded doors and windows
Individually, these upgrades seem reasonable. But once you start selecting what's actually needed for a comfortable workspace, the total price rises very quickly — often to a point where it no longer resembles the headline figure that caught your attention in the first place.
This isn't dishonest marketing — it's just how kits are sold. But it does mean you need to price the finished room, not the starting point.
The three main ways people build an outbuilding
Most people end up choosing one of three routes. Each has its place — but the costs behave very differently.
1) DIY timber-frame build
This is the most flexible option and, if you're prepared to do the work, often the most cost-effective.
You source materials yourself: structural timber, sheet materials, insulation, roof system, cladding, doors and windows, fixings and membranes. You then build it yourself, sometimes bringing in paid help for specific tasks like the base, plastering, or roofing.
Typical DIY cost ranges (UK, 2026):
- Materials only (timber frame, insulation, roof, cladding): ~£500–£650 per m²
- With foundation and electrics (fully built, DIY labour): ~£700–£950 per m²
- High-spec finish (premium cladding, upgraded glazing): ~£1,000–£1,400+ per m²
Example: A 3m × 4m (12m²) fully insulated office costs £6,282 in materials, £8,500–£11,000 including foundation and electrics.
The wide range reflects just how much control you have over specification — and how quickly costs move when you change timber sizes, insulation thickness, glazing, or cladding.
2) Supplied & installed garden rooms
This is the lowest-hassle option. A company designs, manufactures, delivers, and installs the building for you.
The price reflects more than materials: labour, design time, overheads, warranties, project management, and often full electrics and heating.
Typical installed costs: Often quoted in the region of £1,700–£2,200 per m², with bespoke or premium builds going higher.
You pay more, but you get speed, convenience, and someone else carrying the risk.
3) Log cabin kits
Log cabins sit somewhere between DIY and turnkey builds. They're usually sold as pre-cut kits, often with attractive entry pricing. For simple garden buildings, they can be excellent value.
Where people get caught out is assuming the kit price equals the finished cost.
Once you add a proper base, insulation suitable for year-round use, roofing upgrades, internal linings, and better doors and windows, the total cost can end up surprisingly close to a timber-frame DIY build — sometimes without the same flexibility in layout or insulation depth.
One cost that almost everyone underestimates: electrics
Whether you're building from scratch or assembling a kit, electrics are an additional cost that applies to almost every garden office build — and it's not one you should try to cut corners on.
If you want sockets, lighting, heating, or a data connection, the electrical work must be carried out (or at least signed off) by a qualified electrician.
In the UK, this isn't optional. Electrical work needs to comply with Building Regulations, and at the end of the job you should receive the appropriate electrical safety certificate. This is important not just for safety, but also for insurance and future house sales.
A few key points that often surprise people:
- Electrics are rarely included in DIY material costs
- Kit and log cabin prices almost never include full electrical installation
- The cost depends heavily on distance from the house, trenching requirements, and consumer unit capacity
For budgeting purposes, electrics can easily add hundreds to a few thousand pounds, depending on scope. It's one of the reasons two "similar" builds can end up with very different final totals.
A realistic comparison: 3m × 4m garden office (12 m²)
To make this concrete, let's look at a common size: a 3m × 4m garden office.
DIY timber-frame build
Using actual material costs from a fully insulated build specification:
- Materials (timber, boards, insulation, roof, cladding, fixings): £6,282
- Foundation (concrete base, pads, or screws): £1,000–£2,500
- Electrics (qualified electrician, armoured cable, consumer unit): £800–£2,500
- Total DIY build cost: £8,500–£11,000
This is for a properly insulated, office-ready build using standard UK timber frame construction. The range reflects choice of foundation type and electrical complexity.
Supplied & installed garden room
At typical installed rates, the same size often comes in around £20,000–£26,000+, with electrics usually included as part of the package.
That's roughly 2–3× the cost of a DIY build — though you're paying for professional installation, warranties, and avoiding all the project management yourself.
Log cabin kit
The kit alone might appear much cheaper at first. But once you price a usable, insulated, office-ready finish — including electrics — the all-in cost often ends up surprisingly close to a timber-frame DIY build, sometimes without the same flexibility in layout or insulation depth.
Where the money actually goes in a DIY build
One of the biggest lessons I learned is that most overspends come from the same few areas.
1) The base
Concrete slabs, ground screws, or paving systems can vary massively in cost depending on site conditions and access.
2) Structural timber and boards
This is the backbone of the build — and where timber price changes hit hardest.
3) The roof system
Flat roofs range from very basic to very robust. EPDM, insulation build-ups, trims, and detailing add up quickly but pay off in longevity.
4) Cladding
Cladding is effectively an "aesthetic multiplier". The same structure can cost very different money depending on what you wrap it in.
5) Doors and windows
Glazing is one of the fastest ways to increase costs — structurally and financially.
6) Making it an actual office
Insulation, vapour control, internal linings — and electrics — are what turn a shed into a workspace.
Why timber prices matter more than people think
Timber isn't just one line item — it influences wall framing, floor joists, roof joists, noggins, battens, and often cladding and trims.
Over the last decade, UK timber prices have risen significantly in real terms and have also become more volatile. That volatility is why people's build experiences can differ so dramatically depending on when they built.
This is one of the biggest reasons historic build costs don't translate well to today's projects.
The real problem: nobody prices the whole build
The pattern that kept repeating was this:
- Inspiration pricing was either incomplete or outdated
- Kit pricing focused on entry points, not finished rooms
- Very few examples broke down the entire material stack and services
Without a full breakdown, it's impossible to sanity-check whether a number makes sense for today.
That gap — between "this looks affordable" and "this is what it actually costs" — is what led me to start building Outbuilding Planner.
Final thoughts
Building a garden room or outbuilding can still be excellent value — especially if you're prepared to DIY part or all of it.
But the key is pricing the real build, not the idea of one.
Don't budget based on inspiration pricing. Budget based on today's materials, today's specifications, and the full scope of work — including electrics.
That's the difference between a project that feels stressful and one that feels under control.