Report Model, Which Approach?

Hi All,

I'm a newbie to Report Model and not able to find some conceptual information, Can you guys answer following:

I€™ve

Employee [Name]
->Employee_Days [Day] (1-*)
->Employee_Day_Activities [Activity_Type, HoursSpent] (1-*)

schema and a generated model out of it. Now I€™ve few report requirements which will be developed based on Report Model. These Reports needs aggregate of All similar activities and the hrs spent and it'll be shown with every employee. Like Employee Xyz has spent 14 hrs total on Sick Activity, which will be shown as

Employee Sick Hrs Maternity Hrs WorkHrs
Xyz 14 0 20

Now i need to know the approach to develop it like i'v to ways in my mind

- create 3 custom fields(Sickhrs,Maternityhrs,Workhrs) in the Employee Entity(model), so that managers can create reports like above by simple drag and drop

- leave model as it is.. just create more descriptive fields in all the three table and let managers do the activity grouping etc to develop report like above..

Which approach should i follow? Moreover can you point me to some conceptual info like how report model works..etc..

regards
faraz