The BIM Workbench imports tools from the Draft Workbench, as it uses its 2D objects to build 3D parametric objects. But it can also use solid shapes created with other workbenches like Part and PartDesign.
The developers of Draft and BIM also collaborate with the greater OSArch community, with the ultimate goal of improving building design by using entirely free software.
Getting started
When starting the BIM workbench for the first time, a welcome dialog is shown, giving a quick overview of how the workbench works, and allowing the user to start an in-game tutorial. The welcome dialog is also available from the help menu. When the welcome screen is closed by clicking OK, the BIM setup dialog will be shown, that allows the user to quickly set some of the most common BIM-related preferences of FreeCAD without the need to browse through the full FreeCAD preferences pages.
The BIM project setup tool allows you to quickly setup a BIM project by entering some basic information about your project. You can then, for example, use the different 2D drafting tools to sketch guidelines and baselines, then use the different 3D modeling tools to automatically build 3D BIM objects from them. A line, for example, can become a wall simply by selecting it and pressing the Wall button.
Common building elements such as walls or columns are easily created by pressing the appropriate toolbar button and clicking points in the 3D view. They can be moved, rotated and edited once created. Most BIM elements are created on the current working plane, so a typical workflow involves placing the working plane first, then creating a BIM element. More complex elements can be created by drawing 2D elements first, then using one of the BIM tools to convert them into the desired element.
Elements of building projects can be organized using sites, buildings and levels, to reproduce what is commonly done in other BIM applications. In FreeCAD, however, such structures are not mandatory, and you are free to organize your model elements as you see fit, for example using groups.
2D drawings can be generated from a model to represent plan, section or elevation views. To generate such a drawing,section planes are placed in the model, to indicate where it should be cut or viewed from. Once the section planes are in place, two methods are possible:
Create projected views in the document using shape views, then add all the necessary annotations such as texts and dimensions, then put all this on a page. This is the recommended way, as it offers more flexibility.
Create a view on a page directly from the section plane. Then all the needed 2D annotations must either be added to the section plane, or done directly on the page. This is less flexible.
Finally, quantities schedules can be created using the schedule tool.
The in-game tutorial is an easy way to quickly get on track with the BIM workbench.
Tools
The BIM workbench gathers tools from several other FreeCAD workbenches, mainly Draft and Part, roughly reorganized in logical categories.
Additionally, if such addons are installed, tools from Reinforcement (extra reinforcing bar tools), Fasteners (bolts and screws), Flamingo/Dodo (metal structure and piping tools) and Parts Library are automatically included in the BIM workbench.
The BIM workbench also adds a series of items in the status bar of FreeCAD, and a couple of context menu items, accessible by right-clicking in the 3D view or in the tree view.
2D drafting
2D objects are commonly used as drafting aids, or to draw base lines and profiles to build BIM objects on. They can also be used to draw symbols and annotations in your model. Apart from sketches, that use their own coordinate system, 2D objects will be drawn on the current working plane.
Sketch: Creates a new sketch and enters sketch edit mode. Sketches are advanced 2D objects with constraints support.
Component: Creates a non-parametric Arch component.
External reference: Links objects from another FreeCAD file into the current document.
Annotation
Annotations are visual help objects that can be placed inside your model. They can be used to export your model directly to a 2D format like DXF, or reused when creating 2D views of your model with the TechDraw Workbench.
Text: Creates a 2D text in a document or on a TechDraw page.
Shape from text: Creates a compound shape that represents a text string.
Aligned dimension: Creates a dimension aligned with two points or a selected edge.
Horizontal dimension: Creates an horizontal dimension between two points or from a selected edge.
Vertical dimension: Creates a vertical dimension between two points or from a selected edge.
Leader: Creates a 2-segment polyline with an arrow at its end, to be used as a leader line in conjunction with a Text.
Label: Creates a multi-line text with a 2-segment leader line and an arrow.
Offset: Offsets each segment of a selected object over a given distance, or creates an offset copy of the selected object.
2D Offset...: Constructs a parallel wire at a given distance from the original, or enlarges/shrinks a planar face (parametric version). This is the same tool as Part Offset2D.
Cycle background: Cycles between vertical gradient, radial gradient and simple color background modes. This can be used to toggle between a dark background for modelling and a white background for 2D drawing.
Arch 3Views: Creates top, front and side views from a mesh. Not available in 1.0 and above.
Arch BuildingPart: Creates a building part including selected objects. Not available in 1.0 and above. Use Arch Floor instead.
Arch CloneComponent: Produces Arch Components that are clones of selected Arch objects. Not available in 1.0 and above. Use Draft Clone instead.
Arch CutLine: Cuts an object according to a line. Not available in 1.0 and above. Use Arch CutPlane instead.
Arch MultiMaterial: Creates a multi-material and attributes it to selected objects, if any. Not available in 1.0 and above. Use BIM Material instead.
Arch Project: Creates a project including selected objects. Not available in 1.0 and above. Use BIM Project instead.
Arch SetMaterial: Creates a material and attributes it to selected objects, if any. Not available in 1.0 and above. Use BIM Material instead.
Preferences
Preferences: General preferences for the BIM Workbench.
Fine tuning: Extra parameters to fine-tune BIM behavior.
Working with IFC
The BIM workbench works natively with Industry Foundation Classes (IFC) files. Native means there is no more translation between the IFC contents and FreeCAD: The IFC contents are directly rendered in FreeCAD, and any change affects the IFC contents directly. Read more on NativeIFC.
If you don't plan to work with others, and have no need for IFC, you can still use the BIM workbench tools and simply ignore anything related to IFC. You can still export your model to IFC anytime.
The old Arch IFC importer is disabled by default in FreeCAD, but still available from Python.
There is also a specific NativeIFC Tutorial that explains the concepts further.