What design pattern to use for a web based application?

I want to know the appropriate design pattern that can be employed for a Web based application described as below:

The application mainly consists of 4 roles: Admin,Salesproviders ,Salesmen and Customer. Out of which, customer won't have a login.

The admin Role can be further broken down into two sub roles-HomeAdmin, ExternalAdmin.

The admin(any one of the two sub roles) will assign tasks to the sales providers and monitor their working.

Salesmen will be handled and assigned trips by the sales providers.It is the sales men who will feed maximum transaction data into the system. This will include their door-to-door services, customer hits and customer misses.

As per my understanding, on a very high level I can think of abstraction of each role into an interface with various implementation classes.

The key in the application is that the admin should be able to pluck out reports from the application which will feature various metrics like- total no. of salesmen, total number of customers, hits of the month, misses of the month. This reports related interface should be highly flexible-liable to change every week. How should I go about doing this?