How to Create a 3D Sketch Building in Autodesk Forma Site Design

Learn how to create a 3D Sketch Building in Autodesk Forma Site Design using the 3D Sketch tool. This step-by-step tutorial covers how to build and refine a 3D massing model, create different roof forms, add curved geometry, and convert your model into a building with defined floors, functions, and area metrics.

Whether you’re exploring early-stage architectural concepts or developing a building massing study, 3D Sketch gives you the flexibility to shape and refine your design directly in Forma Site Design.

Step 1: Create a Basic 3D Shape

Start by creating the initial geometry for your 3D massing model.

1. Launch 3D Sketch by clicking New 3D Sketch in the Design toolbar.
2. Select the Cuboid tool from the 3D Shapes menu and draw a cube measuring 40 feet.
3. Select one of the cube’s faces and click again to extrude it by 100 feet.
4. Repeat the process in the perpendicular direction to create a square footprint for your 3D volume.

You now have a basic 3D form that you can modify and develop into a more detailed building concept.

Step 2: Refine Your 3D Massing Model

Use the tools in 3D Sketch to create more complex geometry, explore different roof designs, and add architectural features to your building mass.

Extrude Faces to Shape Your Design

1. Select the Line tool and draw lines between existing edges to divide the roof into two surfaces.
2. Select one of the newly created surfaces and click again to extrude it downward through the volume.
3. Repeat the technique on vertical surfaces to further shape your 3D massing model.

Pro tip: Snap to edge midpoints when drawing lines to improve accuracy and maintain control over your geometry.

Create a Pitched Roof

Add a pitched roof to introduce more variation to your building design.

1. Use the Line tool to divide part of the roof into a square or rectangular surface.
2. Select the new surface and extrude it upward by 20 feet.
3. Draw a line on the surface to define the roof ridge.
4. Select the roof edges running parallel to the ridge line.
5. Use the Move tool to move the selected edges downward along the Z-axis until they align with the rest of the roof.

Pro tip: Hold Shift to lock the movement direction while repositioning the edges.

Create an Asymmetrical Angled Roof

Explore a more dynamic roof form with an asymmetrical angle.

1. Use the Line tool to divide part of the remaining flat roof into a square or rectangle.
2. Select the outer edge of the newly divided surface.
3. Extrude the edge upward along the Z-axis to create the angled roof geometry.

This technique allows you to experiment with different roof profiles during early-stage design exploration.

Add Curved Geometry

Introduce curved elements to create more varied building forms.

1. Open the Sketch menu in the toolbar and select Arc by Three Points.
2. Place the first two points so they intersect the roof edges.
3. Position the third point to define the desired curve.
4. Select the surface outside the arc and extrude it downward to your desired level.

You can use this technique to explore curved rooflines and other distinctive massing features.

Step 3: Convert Your 3D Volume into a 3D Sketch Building

Once your 3D geometry is ready, convert the generic volume into a 3D Sketch Building to define floors and review building area metrics.

1. In the right panel, click the plus (+) icon next to Add floors.
2. Floor lines will appear on your 3D volume, showing how the default floor heights are distributed throughout the design. Your Generic 3D Sketch is now a 3D Sketch Building.
3. In the Floors section of the right panel, adjust the total number of floors, default floor height, and individual floor heights as needed.
4. Review the building’s Area metrics in the right panel to understand its floor area.

Note: Area metrics are calculated only for buildings located within a defined Site Limit.

Step 4: Assign Functions to Building Floors

After converting your model into a 3D Sketch Building, assign functions to individual floors to organize the proposed building use and review the corresponding area breakdown.

1. Exit 3D Sketch by pressing Esc or clicking the X in the toolbar.
2. Select one or more floor volumes in your building.
3. In the right panel, assign a Function to the selected floors.
4. Expand Gross Floor Area under Area metrics to view the area breakdown by function.

Assigning floor functions helps you organize your building programme and evaluate how space is distributed across different uses during the early design phase.

Conclusion: Explore Building Concepts with Autodesk Forma Site Design

With the 3D Sketch tool in Autodesk Forma Site Design, you can move beyond simple building volumes to explore more detailed massing concepts, experiment with roof forms, define floor configurations, and review area metrics—all during early-stage design.

By combining flexible 3D modelling with building-level information, architects and designers can explore design possibilities more efficiently and develop a clearer understanding of their concepts before moving into the next stages of planning and design.

Ready to explore what’s possible? Discover Autodesk Forma Site Design and start developing your next building concept with a smarter, more flexible design workflow.