I have made a few aquarium stands, but always the same size as the tank. However, if you put a 3/4" plywood top on the stand a 55 gallon tank shouldn't be a problem on a wider stand. 55 gallons of water weigh less than 500 pounds, or less than two big men standing side by side. When you look at it that way the weight doesn't seem so forbidding.
The neatest design I have seen, and what I used for my current stand, uses 2 by 4's or 2 by 3's with half lapped joints to tie all the ends together. (At the corners the half lap joints go two ways, leaving each leg with one quarter of the material left at the joint). Then a 3/4 plywood top distributes the tank weight over the four legs. Where a shelf is needed at the bottom you half lap joint a ring around the legs. That makes a very sturdy, steady, no racking stand. For appearance purposes you then cover the outside with good looking plywood or hard board, if you paint it. Add a door or two in front and you have a very, very sturdy and nice looking stand. I have a link to an article by the designer of this somewhere if I can find it.