Garden Rooms & Outbuildings
Garden Room Cost Estimator
Costed bill of materials for a garden room
Updated 12 July 2026 · Live
What this tool does
Builds a costed bill of materials for a garden room — base, frame, cladding, insulation, roof, glazing and labour — with a contingency and cost per m².
Enter the cost of each element plus labour and a contingency; the calculator totals the build and the cost per m².
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Formula Used
Builds a costed bill of materials for a garden room — base, frame, cladding, insulation, roof, glazing and labour — with a contingency and cost per m². It runs entirely in your browser and shows the working, so you can check every step against your own figures.
How the garden room cost calculator works
Each element — base, frame, cladding, insulation, roof, glazing — is a line you price, added to your labour figure. The subtotal is grossed up by the contingency to a total, and the total is divided by the footprint for a cost per m² you can compare against off-the-shelf garden-room prices. Every figure is yours to enter.
What you enter
Enter the cost of each element plus labour and a contingency; the calculator totals the build and the cost per m². Every field is editable, and the result recalculates the moment you change a value.
Reading the result
The line breakdown shows where the money goes and lets you test a cheaper cladding or a bigger glazing spend against the total. The cost per m² is the number that compares your self-build against a supplied-and-fitted quote.
Safe by design
This tool counts materials and cost. It never sizes the structural frame or the foundation loads — where those matter, a structural engineer signs them off.
Assumptions and limits
Prices are your own — nothing is baked in, because garden-room costs vary hugely by spec, size and region. The estimate excludes planning or building-control fees, services (power, water, data) and any landscaping, which differ by site.
Using it with the rest of BuildMetricLab
This calculator is one step in planning the job. Pair it with the related tools in this category and across BuildMetricLab to go from a single figure to a full costed plan — a sizing figure feeds a cost estimate, a cost estimate feeds a project budget, and each result carries straight into the next tool. Every BuildMetricLab tool runs entirely in your browser — no sign-up, nothing sent to a server, and the formula is shown on the page so the maths can be audited.
Sources & methodology
Builds a costed bill of materials for a garden room — base, frame, cladding, insulation, roof, glazing and labour — with a contingency and cost per m². Every result is calculated from the values you enter, all inputs are editable, and no time-sensitive prices or rates are embedded.
Frequently asked questions
What does a garden room cost per m²?
It varies enormously with spec — from budget self-builds to fully insulated, glazed studios. Enter your own element costs and the tool gives your figure.
Does this include services?
No. Power, water and data connections vary by site and are not included — add them as separate figures.
What contingency is sensible?
A 10–15% contingency covers access issues, spec changes and the unexpected. First-time self-builds justify the higher end.
Are approvals and permit fees included?
No. Many garden rooms may qualify as exempt or complying development depending on size and location, but rules vary by state and council — confirm locally and add any permit or certification costs separately.
Spotted something off?
Calculations or display — let us know.