I built a ship with what I thought were going to be aesthetics, trying to utilize the 7 units up, and 7 units out each direction, it doesn't look good in any form IMO unless you base your design on a TIE fighter offshoot like some did. I don't want to build a big ship, I just don't want to build a good looking ship that isn't going to get creamed by the fatter TIE fighter version. You could say, Maximum length or width of say, 12, with a 350 block count max for class 1. 7x7x7 = 343 blocks. 11x11x11 = 1331 blocks, and 15x15x15 = 3375 blocks. Set one maximum dimension if you want to have them fit inside a certain docking area, but the block limits will make it more fair and give you better results.
Or, you could keep the dimensions as you have now, and then reduce the maximum block count to a percentage of the total volume (which might disqualify some current entries). But either way, you'll have better LOOKING ships that will for all intents and purposes have an equal fighting chance based on the builder's skill.
I know there's no prize, but I really want to show off my skillz on this competition. I don't want to have a rubber ducky looking bathtub ship, or a tie fighter cube.