The object of the exercise is to estimate the cost to the employer of their desired scheme. It usual to base the pricing of such estimates on historical cost date gleaned from the analyses of the costs of similar buildings adjusted to account for any fluctuations in price levels and for project idiosyncrasies.
The accuracy of the estimate will be influenced by the state of the design information, both drawing and specification notes. A preliminary estimate is often required when there is little or no information available, so it is usual to base such an estimate on place costs or net area/volume costs. as the design information is developed it is possible to produce more refined estimate based upon element unit quantities or measured approximate quantities. Finally, when the design an even more accurate estimate can be achieved by basing it on the measured accurate quantities in the bills of quantities.