Steve,
Take the tutorial on creating families.
Use reference planes to define your geometry. "Load from Library" the beams you plan to use, use the componet command to place them, & lock them to the reference planes.
If you want to use the beam tables in your family to select the beam size, you'll have to define a parameter in your portal family that has the same name as each of the beam parameters, then select the beams, go to properties, select edit, and using the "equal" button, match each beam parameter to the new portal beam parameter.
Then go to the directory where the beams are stored, find the .txt file associated with the beam you used (same name, only .txt extension), and make a copy of this file giving the same name (.txt extension) as your new portal family.
If you plan to have more than one size beam in the family, think about it. I'm sure there must be a way...
