A quiet office at the bottom of the garden is an appealing answer to the kitchen-table working day. The temptation is to see a starting price, picture a finished room and mentally book the delivery. The missing step is working out what that price buys.

A kit and a completed room are different purchases

Checkatrade’s June 2026 table lists mini garden-office kits delivered for self-assembly at £2,500–£8,000, with assembly labour at £700–£1,800. These are national guide figures, not BOL prices. The table does not state its VAT treatment; confirm it when comparing quotations.

The useful comparison is therefore not “kit versus extension”. It is the total cost of each option at the point you can use it. A complete quotation should say whether the room is ready for furniture or still needs several trades after the structure arrives.

Write a ready-to-use brief

List what the room must do rather than choosing the cladding first. Two people taking calls need a different arrangement from one person answering emails. A desk, chair and monitor also take more usable space than an empty showroom suggests.

• Ground and access: base design, site preparation, delivery route, removal of surplus material and making the garden good.
• Comfort: the specified wall, roof and floor build-up, ventilation, heating and shading.
• Services: power, lighting, data connection and any plumbing, including their routes from the house.
• Completion: decoration, floor finish, steps, paths and clear responsibility for each item.

For a narrow London terrace, delivery access may shape the construction method. On a sloping Kent garden, the level change may influence the base and the route to it. Ask the installer to assess the actual site before accepting a package total.

Decide what the room is allowed to be

Planning Portal’s outbuilding guidance distinguishes incidental garden uses from separate self-contained living accommodation. Turning an office idea into somewhere somebody sleeps is a meaningful change to the brief, not simply an extra item of furniture. Planning and building-regulations checks must match the proposed use.

If the aim is occasional desk space, compare this with our home-office and guest-room ideas. If it is a permanently occupied living space, discuss the requirements alongside an extension. Cost the same usable outcome before choosing the solution.