Designing and creating the aggregate tables is not an easy task. Especially, creating the aggregate dimension tables and aggregating the fact tables will take some time. You'll have to think about the joins as well.
There's a utility called Aggregate Persistence in BI Administration Tool. This utility will help us create the aggregate tables and load the precomputed data into them automatically. But you'll have to reflect all changes to the ETL process. Once this wizard is executed, the aggregate tables are going to be created in the database. Also, summary data will be calculated and it's going to be inserted into the aggregate tables. Obviously these tables should be imported into the BI repository and the physical joins should be created. These two steps are going to be done automatically too. The next step is reflecting the changes in the BMM Layer. Actually, Aggregate Persistence Wizard will do this task too. As a summary, it's a completely automated...