Working with an interior designer: what to expect, and what to ask.

Very little of it is choosing cushions. The bulk of the work is decisions and coordination: how the rooms should be planned, what can and cannot be changed, what the builder needs drawn, what to order and when it has to be ordered by. A good designer saves you from the expensive mistakes — the layout that was never going to work, the sofa that does not fit round the turn in the stairs, the sockets behind the new joinery — and then makes the result look effortless, which is the part everybody sees.

• Plans the space before decorating it
• Draws what the builder has to build
• Specifies, sources, orders and tracks
• Carries the decisions so you do not have to

Earlier than feels natural. If there is building work, the ideal moment is before the architectural drawings are fixed: moving a doorway costs nothing on paper and a great deal once the wall is plastered. If it is a decorating project, the useful moment is before you buy anything — most people come to us having already bought one large item that the scheme then has to be built around. It is not fatal, but it is a constraint you did not need to give yourself.

• Before the drawings are frozen
• Before the first big purchase
• Before the builder starts pricing

Not very much, and certainly not a finished vision. Photographs of the rooms as they are, any existing floor plans or an estate agent's plan, a rough sense of the timescale, and — most usefully — a list of the things that irritate you about the house day to day. The complaints are more revealing than the inspiration. If you have a Pinterest board, bring it; if you do not, no matter, that part is our job.

• Photos of every room
• Any existing plans
• A list of daily irritations
• Your honest timescale

Ask who will actually do the work and who you will be dealing with day to day. Ask whether they produce technical drawings or hand the builder a mood board. Ask how they charge, and at what point each stage commits you to the next. Ask to see a project of a similar type — a period property is a different discipline to a new-build. And ask how sourcing and procurement are handled, because that is where the time goes and where things quietly go wrong.

• Who will I actually deal with?
• Do you draw for the builder?
• How does each stage commit me?
• Who handles orders and deliveries?

Older houses ask for more drawing, not less. Floors are rarely level, reveals are deep, chimney breasts sit where they sit, and a room may have been two rooms a century ago. That means joinery is measured on site rather than ordered from a catalogue, curtains want interlining and a heading that suits the window rather than the fashion, and paint colours behave differently in rooms with small windows and thick walls. None of it is a problem; all of it is a reason to plan before buying.

• Nothing is square — measure on site
• Interlining earns its keep
• Test paint in the actual room
• Work with the quirks, not against them

The view out of a window is part of the room. When the garden is being reworked as well — through KB Landscapes, the landscape side of the studio — the two can be planned together: a terrace positioned for the evening sun and for the doors it is seen through, levels resolved against the new floor level, planting that gives the sitting room something to look at in February. It is the one advantage of having the interiors and the landscaping under one roof, and it is worth using.

• Sightlines from inside out
• Levels resolved once
• One programme, not two
• Planting for the months you are indoors