This command creates a rectangular polyline around selected
linework. This can be used to give a building all one
elevation.
In the
Draw Building Envelope dialog box, set the layer for the new
polyline and the desired offset value, (the above example is offset
by 5 feet). Select whether or not to be prompted for
specified offsets for each side, an elevation for the new polyline,
and whether or not to trim existing linework that crosses the new
polyline. Click OK. Select the entities that make up
the building.