Most people arrive with a budget for the building and very little for everything that surrounds it. The building is usually priced accurately. The rest is where projects run out of money, and it is predictable enough to plan for.

Before anything is built. Professional fees, statutory approvals and the council contributions that come with them. Site investigation, which people resent paying for and which is the cheapest insurance on the project. On a plot that slopes or sits on difficult ground, this is also where you find out what the substructure is really going to cost, and it is much better to find out now.

Getting the site usable. Access good enough for a lorry, a water supply, and a power connection. On the edge of the city these are not administrative details, they are line items with real numbers and real lead times. Boundary walls and gates rarely make the first budget and almost always get built.

The part after shell complete. Once the building is weathertight, spending changes character entirely. Everything from there is visible, and every visible thing has a price range rather than a price. The same floor area takes a finish at three very different costs, and the drawings will not tell you which one was assumed. Pricing the shell and the fit-out as two separate exercises is the single most useful thing a client can do.

The tail. A detached staff quarters, landscaping, and the furniture that turns a finished house into an occupied one. And a contingency that is genuinely held back rather than spent early on an upgrade, because the whole value of a contingency is that it is still there in the last month.

None of this is exotic. It is just the part of the budget that nobody photographs.