Well, based on his statement, he already has a silver aro and is trying to build a tank to accommodate it. It doesn't say anything about being new to fishkeeping. Maybe we shouldn't assume that a new member is new to the hobby.
That being said, the important thing to keep in mind when building an aro tank is to maximize your surface area. The tank should be as wide from end to end and front to back as possible. Depth isn't as important.
As far as building it, I'm sure there are other members here that can get you going in the right direction.