Click Isometric Rectangle .
If the Isometric toolbar is not displayed, click Tools > Add-Ins. On the Add-In Manager dialog box, select the Isometric Toolbar Commands check box, and click OK.
To confirm that the isometric rectangle consists of lines that remain connected when you relocate them using the Select Tool command, turn on Maintain Relationships on the Tools menu. If this option is not on, Isometric Rectangle creates a rectangle composed of four separate lines that do not stay connected if you move each line.
Click a point to start defining the rectangle base.
Click a second point to complete the rectangle base.
Click a third point to complete the rectangle.
You cannot drag the pointer to draw the rectangle.
To set the plane on which to place the rectangle, you can set options on the ribbon.