I am asked often how to go about creating a basic family. I created a 2 part video last year for a colleague who was learning Revit. They wanted to know how to build a basic window family. See below for the method I use when creating this family. Over the next few months, I may expand on this example and slowly build varying complexity into the same family.
Creating a Basic Window: Part 1 (Geometry)
Creating a Basic Window: Part 2 (Materials)