a) By keeping a work diary to record how long different jobs take. You can only estimate the time it will take to do a job by using personal experience of this kind of work and by knowing the work capabilities of your staff.

b) Cost of labour
    Cost of materials
    Time involved
    The specifications for the work (whats included / not included etc.)
    Terms and conditions
    GST
   
c) This is an an early calculation of the cost for a project. This calculation is presented before the project has begun, its gives everyone an idea of the costs involved and helps with budgeting in every aspect of the project.