What are the primary goals of creating a building model? Who are the key stakeholders?
The primary goals for creating a building model is to convey, illustrate, and describe the vision of a building. It allows the architect to design the building in a way the is organized, clear, and detailed. It allows those involved in construction to see the exact measurement, materials, and placements of different components of the building. It also allows owners, buyers, investors, and other people outside the composition of the building but involved in the decision making to see very clearly and easily what will be build.
How much detail should you include in your building model? How do you decide?
The level of detail in your building model changes as you progress but also depends on your desired outcome. When you are in the first stage of the design and building process it is enough to have just the outline of wall dimensions, heights, levels, floor, roof. If you are just trying to understand if the square footage and shape of the house will fit in the boundaries that is enough. If you want to progress to what the actually building will look like you should focus on the actual material that you want to use, edit the windows/door/wall shapes, add fixtures, and other features that illustrate what the building will look like. The next stage is looking deeper into the layers of the materials used for the construction, looking at weather and lighting to add feature that enhance that, and add extra details and furniture for the aesthetic appeal.
Many door and window manufacturers provide Revit families for doors and windows that you can specify for your building design.
Manufacturers provide these families so that a building model will accurately represent the features that they will provide. This makes it easier for the architects to design around these features and for those in charge of construction to trust that the rendering is accurate. It also allows designers to browse their categories and perhaps design and add their features in the initial design process rather than in post processing.