1. First you nail down your reporting requirements. Talk to your business users and get defined all the metrics they want to report. 2. Identify the data elements that are required to fulfil the reporting requirements. 3. Create a data model ( models) that supports all the business requirements as well as easy to handle through BO. If you already DONOT have a well designed data warehouse, you may have to create the model for integration layer as well as for presentation layer. In the other words if your data elements are not in a stable base tables, you have to model these base tables as well. 4. Identify the source of the data elements and create the source to target data mapping. 5. Design/ develop your ETL work to load the physical tables. If your base data is already in data ware housebase tables and you decide to create a logical mart on that ( instead of physical datamart), create the logical views to support the mart. 6. Design/ Develop your BO universe. 7. Create your reports using your BO universe.
These are just a few logical flow of activities for creating a datamart. There are lots of other considerations based on your environment and thechnolgy you used for creating a datamart.