What are the primary goals of creating a building model? Who are the key stakeholders?

• What do they care about most?

I feel that a project owner, designers, engineers, builders, operators, and clients would be key stakeholders in a construction project generally. Similarly, I think that in building models that these positionalities remain the same with a little more emphasis on the designers, engineers, and builders.

Many door and window manufacturers provide Revit families for doors and windows that you can specify for your building design.

• What is the advantage to manufacturers for providing these families? (it's not free to create and provide them...)

Through providing these families, a manufacturer is making the investment to essentially get their products seen and interacted with at a higher frequency. Relevant stakeholders would be able to carry out their "test drive" with the product. Making the "test drive" accessible allows the customer to feel safer about their overall decision and I imagine this is ultimately better for business.

What are the advantages of getting the Revit component families (for furniture, equipment, and fittings) directly from the manufacturer versus from an online sharing website like RevitCity.com?

I think that in getting it directly from the manufacturer, you can be more assured that the dimensions of particular components are accurate. Furthermore, through the manufacturer it may become easier to access similar components.