A Quantity Surveyor plays a vital role within the construction process. S/he devises the Bill of Quantities for any large construction job. This outlines in detail the amount of materials which will be required for a job, including any finishings and fittings, right down to the amount of nails (roughly) which will be used.
This enables a contractor to be able to know exactly what will be used and therefore determine how much a job will cost.
S/he will also build in contingency sums, in case things go wrong when the building work commences, due to site constraints etc.
During the works, the Quantity Surveyor will also produce reports on how much has been spent and how much is left in the pot. Thus effectively controlling the purse strings. This will help keep overspend to a bare minimum and could even save money: although a Quantity Surveyor is far from cheap!