Just as important as what convict2161 mentioned ... IMHO .... Is the type of stand. Weight on floors become an issue when you get around a 50gal or larger. The way I figure, if a second floor and support a couch / sofa with 2 adults, it should hold 45gal and down.
With larger tanks... How the weight is distributed becomes an issue. For those tanks, I don't like metal stands that have 4 legs at the corners. That just pinpoints the weight in a small area. Stands that resemble cabinets with a wide base touching the floor better distributes the weight.