This answer currently applies to the Revit 2012 courses and on.
At CADLearning, we create our Revit video training tutorials to meet the needs of users in areas where both imperial systems and metric systems are used. In order to handle both systems of measurement in the same course, we provide imperial and metric exercise files for lessons dealing with units. The files are set up using the respective templates, so that any element can be created at the appropriate units.
Not only do we provide both exercise files, but also, both units of measurement are used in every lesson where specific measurements are called out. For example, if the lesson is about creating a wall, the lesson may state, “sketch a wall 2 feet long (or 600 millimeters in the metric file)...”.
The method of conversion that is used for length is simply 1 foot equals 300 millimeters. We focus on keeping the measurements in whole numbers so that it makes sense with both Imperial and Metric systems. In Revit Architecture, length is the main measurement.
However, in Revit MEP, there are various measurements, such as length, diameter, airflow, pressure, and so on. In these cases, we research standard metric sizes for items such as ductwork and piping instead of converting the units. So, for a 3.5-inch pipe, we would use a 90-millimeter pipe in the metric file instead of converting 3.5 inches to 87.5 millimeters.
To ensure conformity with nominal measurements, we use both US (imperial) and international (metric) references to ensure the lessons and datasets are relevant and useful.