Size of custom made boards?

Hi Guys,

My Dad and I are thinking about building a custom board as a Father-son project. We are trying to determine what the size should be, so I wanted to ask . . .

has anyone ever built a custom board that is about the size of a 620 or 660? Is there much cost difference in materials from that and just upgrading to a 48x24? All the custom boards I see here seem to be rather large. Thanks, Brian