Explain the difference between unit-cost estimating methods and resource enumeration methods. when would you use unit cost? when would you use resource enumeration?

As defined by the source unit-cost is all about estimating the resource cost and the production rate. It is used to give an overall average cost estimation.

Resource enumeration, on the other hand, is used to tell charge rate for work for a group and the productivity it can perform. This is in situations where there is a lot of details and a more detailed knowledge of the unit cost is needed.

Source: Construction ManagementBy Daniel W. Halpin