I would like to create curved, rounded, or bullnose wall corners. How can I do this?

Rounded and bullnose wall corners are easy to create in Home Designer by using small wall segments of curved walls where two straight walls join.
on the wall connection that you want to change from a 90° corner to a rounded corner.
tool, select the wall you'd like to break into two segments, click on the Add Break 
tool, select the smaller broken wall segment and Delete 

or Curved Exterior Wall 
