เดินการประมาณราคาตั้งแต่ Class D ถึง Class A

Record the documents the estimate rests on and the class of the ladder they put it in, together with what is included and excluded, the market conditions assumed and the reason for the contingency carried. Name the design allowance the class expects, and do not state an accuracy range.

เหตุผล: The class is a statement about the documents rather than about the estimator, which is exactly why it is worth writing down. It tells the reader whether they are looking at a number to plan around or a number to commit to, and that is the difference between an estimate that gets superseded and one that gets blamed.

Carry the design allowance for the class as its own line, carry the allowance for identified risks as a second one, and write the reason for each beside it rather than in a covering note.

เหตุผล: The two answer different questions and only one of them shrinks as drawings arrive. Rolled into a single contingency, the design maturing forces you either to cut a number you should keep or to keep one you should cut, and neither version can be explained to the client without explaining the mistake.

Summarise the same cost by building element, so substructure, structure, envelope, internal finishes, services and external works each carry a total and a cost per square metre alongside the trade breakdown.

เหตุผล: A client comparing this scheme against the last one compares elements, because trades shift with the procurement route and elements do not. It is also the fastest way to find the line that is wrong: an envelope rate out by a third is invisible in a trade total and obvious per square metre.

Apply escalation from a dated index series between the date the prices were built and the mid-point of the construction period, and state both dates on the face of the estimate.

เหตุผล: Escalating to the tender date underprices everything that happens after it and escalating to completion overprices half the job. The mid-point is where the average dollar is actually spent, and a reviewer expects to see it, so using it is one fewer thing you have to defend.

Report the newer estimate against the earlier one element by element, separating what moved because the design changed, what moved because the market moved, and what moved because an allowance was released.

เหตุผล: When a Class B replaces a Class C the client asks one question, which is why the number changed. An answer split into design, market and allowance is a conversation about the project. A single variance figure is an accusation looking for somebody to attach itself to.