Here is how to create a pyramid in the conceptual massing environment:
1. In the default 3D view of the mass family template, click on Level 1 work plane to make it active (see fig.1). In the Draw panel, select the Circumscribed Polygon tool. In the options bar, change the sides to 4.
Tip: This is a fast method of drawing a square from it's center.
Figure 1
2. Place and click the cursor at the intersection of the reference planes, hold down the shift key (to constraint the drawing direction) and click on a second point (see fig. 2):
Figure 2
3. Here's the result for a 200' x 200' square (see fig. 3):
Figure 3
4. Click on any of the vertical reference planes. In this case, let's click on the Center (Left/Right) reference plane to make it active (see fig. 4). Select the line tool from the Draw panel:
Figure 4
5. Draw a triangle (see fig. 5):
Figure 5
6. Press the escape key twice to deselect the Line tool. Hold down the option key and select the square and the triangle shapes (see fig. 6):
Figure 6
7. Finally, click the Create Form button from the contextual menu>Form panel. You now have a pyramid (see fig. 7)!
Figure 7
You can also create parameters as you're sketching to control the height, angle and base dimensions. But I'll leave that up to you.