lol they're not talking about the sizes. Each size house goes from different classes from 1 to 5 and each of those classes has a different base amount of gil that they start at. As far as I can tell though the only thing that differentiates a 5th class mansion to a 1st class mansion is the location. First class will be right at the beach and the 5th class will be back further near the mountain using LL as an example.