I don't even have any racks, but I'll try to help. It should be pretty simple, depending on the material your using and the size of enclosure you want. I'd start with one column. Another good idea may be to find the containers you want to use first. I'don't want to say to many obvious things, but here it goes.
Simply cut the uprights first to the proper lengtha and attach horizontal platforms at the correct hieght (leaving room for a breathing space between the cage and the top). Once it's assembled make sure to add a backing for structural support. If you want to you could also add somesthing to lock the cages in place.
That's how I would do it.