You can get the dimensions for these shapes from structural steel suppliers catalogs. The geometry follows industry standards, so one supplier's product should match another's. They may have different material properties according to their alloys, but even this information is similar.
Standard sizes can be found in the Machinery's Handbook and/or Marks' Standard Handbook for Mechanical Engineers.
Pick your favorite AutoCAD source and then import the 2D geometry in .DWG format into sketcher. From there you can save the sketch (.sec format I believe) for use in the future, create a start part with some standard length or if you use a lot of standard lengths in your design you might want to create your parts as a family table. One advantage of the family table approach is that it can be used as a poor mans Interchange Assembly. Another advantage of the family table approach is that changes/corrections will automatically be applied to all family table members. However, if the number of lengths used is constantly increasing I'd avoid creating huge family tables; especially if you're using Intralink.
Using a start part is probably better than saving the sketch. That way you only have to define all your unique company parameters once.
One person, one computer, one licence, no Intralink.
I thought there was a relationship to the dimensions like radius to thickness etc. Write the relations in the model and do a simple family table to generate the part, do up the few profiles I expect to use.
Most of what I do is sheetmetal, I now have to do up a drawing for one of the field engineers for an antenna bracket to mount on a water tower per a customer request. Maybe he has a buddy with a welding shop.