How to do Activity resource estimation

This is important to remember that the project manager need to first define the work packages and identify the activities and then to identify the resources. Project cannot be planned based on what the resources are available but they need to be estimated and brought together to complete the project. Resources can be material, machinery or the human. It is very important that the resources are estimated and controlled very carefully otherwise they might be allocated to other projects when they are needed for your project.
Project manager need to review the availability of the resources and decide the duration and quantify the requirement of the resources for the project. Similar resources should be put together so that they can be managed and shifted internally as the need of the project may be.