Start with the space you need around the building, not the largest footprint that can be squeezed between two fences. A summerhouse needs room for assembly, an opening door, rainwater management and future treatment.
Use the garden fit checker for a first practical envelope, then compare it with the maker's exact base and roof dimensions.
External size and usable room are different
Retailer dimensions may refer to the base, wall exterior, roof or nominal model size. Those measurements are not interchangeable. Ask for a dimensioned drawing showing:
- the base footprint;
- external wall dimensions;
- maximum roof width and depth;
- internal usable dimensions;
- eaves and overall height;
- door width, position and opening direction.
Use the largest external dimensions to test the garden. Use the internal dimensions to plan furniture.
Make a floor plan with real furniture
Masking tape on a patio is more useful than a model name. Mark the internal wall line, then place paper or cardboard shapes for the main furniture. Leave a clear route from the door and enough space to pull out chairs.
A corner model can use an awkward view well, but its internal wall runs may be shorter than the headline width suggests. A rectangular building is often easier to furnish. Neither is automatically more space-efficient.
Keep access on the outside
Timber hidden hard against a fence is difficult to treat and inspect. The right maintenance gap depends on the building, fence, tools and access method; there is no universal magic number. Choose a gap you can genuinely reach through.
Check the door swing separately. French doors can claim a surprising patch of paving, while inward-opening doors take space from the room. Roof overhang and guttering can extend beyond the wall line.
Delivery access can set the real limit
Measure gates, alleys, corners, steps and overhead obstructions. A building that fits the plot may still be impossible to carry there in its supplied panel sizes. Ask the manufacturer for the longest and widest component before ordering.
Convert feet and metres carefully
Traditional model names often use feet while technical drawings use millimetres. Treat the name as a label. For rough orientation, 8 ft is about 2.44 m and 10 ft is about 3.05 m, but order and build the base from the maker's stated metric dimensions.
Plan the base after choosing the exact model
Do not pour a base from a category-page dimension. The support pattern may relate to bearers as well as the outer footprint. Once you have the installation drawing, use the base size calculator to record the finished size and allowance.
The next practical move is simple: draw the room at full size, open the imaginary doors and walk around it.