System design
To simulate technical layout (design) of a system being projected, UML models and other notations (IE, IDEFx, etc.) are used. Such models can refine functional/non-functional requirements, however it's very inconvenient to work with them if the number of elements is big. Besides, design items can have many specific attributes which need to be registered, used, and analyzed.
To store and account for design items of a system being projected, use Components module. This is a hierarchical view of design items, such as technical subsystems, modules, entities, objects, etc. "Component type" dictionary allows to generate the required nomenclature of the used design items. Using Settings - Attributes module, you can specify additional custom attributes which can be either specific for particular component types or common for all component types.
Tracing to requirements
Relationship with source requirements allows to document important requirements to design items. There is a "many-to-many” relationship between components and requirements.
Relationships between enhancements (user stories) and components allow to document implementation impact of these requirements on the particular components (design items) of the system.
Diagrams
For better communication, create diagrams that display the selected components and the relationships between them. You can choose a class diagram or a component diagram as notation. The diagram view can be set for a specific type of component.
The diagram can be placed into the requirement using the "Insert Module/Report" toolbar button. At the same time, the chart elements are clickable and allow you to quickly switch from a requirement to a specific component.
Cost
Using Budgeting module for a component, you can specify a price value which forms the cost based on the applied components. Budgeting module has a separate article which sums up cost of the solution components. It's important if you use external paid components, or technical devices (servers, computing equipment, or electronic components) in your technical solution. Taking these components into account will help to plan project budget better.
Cost of the components that contain nested (child) components includes their cost.