Modelling vs Drafting
This is one of the most common discussion points for Revit. The answer is dependent on the answer to several other questions:
These questions and answers are broken into more detail below and also break down into deciding on the level of detail.
Ask these questions
What does the BIM Management Plan (BMP/BEP) specify?
The BEP should detail what elements are to be modelled and to what Level of Detail (LOD). If this document specifically says this should be modelled, then you have your answer. If it’s unclear then you’ll need to dive further into the following questions.
Will this element be a clash detection/coordination issue and if so, how detailed does it need to be modelled for this purpose?
If the element has the potential to cause coordination problems, then it is strongly recommended that is modelled so it can be coordinated in 3D. However, the it may not require a high level of detail. This could be achieved as a simple box, but if its more complex and other elements wrap around it closely or certain parts of it need to be accessible for useability and maintenance than it may require additional detail.
Is this element likely to move several times or move with other elements?
If the element has the potential to move several times or hosted to other elements it may become tedious or a potential coordination issue to manage a 2D representation. In which case it may be beneficial to model the element.
Do I need quantities of this element?
If quantities are required then it will need to be modelled, but as above it could be done so generically.
Do I need volumes/weights/areas of the materials that make up this element?
To extract this information a more accurate model will be required.
Do I need to do detailed renderings/visualisations of this area of the model?
This will require communication and coordination with the visualisation artist. They will likely have many resources for fitting out a space, and as such not all information will be required in the Building Information Model. For example, furniture and entourage. However, they will require information on the building form, and material intent could be simply noted.
If they will not be placing any of the fitout, then yes it will need to be temporarily included in the BIM.
Will it affect things like energy analysis?
All shading faces/surfaces and glazing should be modelled to produce an accurate energy analysis.
Do the elements need to be fabricated from the model?
The highest level of modelling is required to produce fabrication documentation. For accuracy purposes, 2D documentation is deemed insufficient for this.
How many views are you going to see it in?
If you are going to see it in more than one view than ideally it should be modelled as this will limit your manual coordination issues.
In some cases this replication could be achieved with a detail group or detail item family, so you must also consider how difficult is this item to model. For example, Ceiling Hangers. You would likely see them in many views, but those views would always be details, and their positions can generally be adjusted to avoid obstructions. Therefore, a detail item would be sufficient.
At what detail levels are you going to see it in?
If you need to see it at a fine level of detail then you could model it in such a way that its only generically modelled in 3D but has symbolic representation built in for a more detailed 2D display.
As above, if all the views are 1:20 Details or below, and the elements are not a coordination issue, then it would be best practice to use a Detail Item family to represent the element.
Is file size an issue?
On a large project, families and modelling needs to be optimised to maintain efficiency but still achieve the desired level of output. This may mean 3D boxes with 2D symbolic representation in Plan/Elevation/Section.