Ytechconst:

Electrical & Plumbing works are usually Billed in Provisional Sum as they cannot be measured accurately, so all you need to do is to get estimate of materials required from experienced electrical engineers & plumbers who have skill in major site works, then you come to a conclusion and procure the materials yourself, then you will have to monitor the materials as they use it, if its not enough then you procure more.

The only thing that can be measured properly here are the electrical & sanitary fittings because they are enumerated items and you can easily determine the numbers required and the cost can be determined by the quality required either China, British etc.

electrical works is usually in three stage: piping, wiring and fittings, while plumbing is in two stages: piping and fittings.