In Solidworks, a 2D or 3D sketch is created. You then choose your frame material from a list of common profiles (such as 1" X 1" X .125 angle iron or 2" X 0.625 wall tube). The profile then gets extruded along the lines of your original sketch. There are simple options for adjusting how the orientation of the profile and for controlling what happens at the corners. Cut lists are automatically generated from the model.
This is a fantastic tool for welded frames, but I have also modified it for use with construction projects and dimensional lumber.
I am sure there is similar functionality in Inventor, but I have no experience with it.