Ted Kruysman shares a method he uses to increase the size of 3D objects.
"When I want to lengthen a 3D object, I copy it and move the end of the copied object to the desired position. If there is a gap between the original and the copy, then I copy a third or fourth time and overlap each segment. Then I use the Union command to make all the copies into one solid object again. This also works to make the object wider or taller."
Notes from Cadalyst Tip Patrol: This works great when there is a flat edge to work with and to align the objects with. It is very quick and easy to do. You can also use the PressPull command or the Extrude command to lengthen a face, but sometimes you need more than a face.