It highly depends on how it’s built, as small changes in steel can mean a lot of weight. Basic rule of thumb is 1/4 inch thick plate is 10 lbs per square foot, steel is 490 lbs per cubic foot, and you can extrapolate from there. Aluminum is 3x lighter and 3x pricier. The basic common plate dimensions are (4 or 5) x (8 or 10), but i could get 10x20 delivered if i wanted to throw lots of money at them.
I chose 16x16 because they potentially make nice building blocks, and fit inside 20x20 squares. Two make a 16x32 (or 16x40 with a center moon pool). “Framing” steel comes in 20ft lengths, so a 20x20 is just as do-able.
If you are a baystead with 3ft of freeboard, you can prolly build the whole thing from deck up with normal home building materials, subject to extreme hurricane standards (glue, clips, rods, diagonals, etc). But 16x16 may be hard to stuff down the ICW for relocation.
As a drydock deck, it can be built to tolerate random point loads of tripod jacks, or the distributed load of air bags, or large lumber, or have specified load points. A residence can be thinner plate all over. The drydock may have no walls above the deck (or any fixed roof), the residence will have walls and roof of various thicknesses depending on strength needed. Ironically, if you shrink the residence to 10x40, a huge amount of the load can be shed to the walls instead of framing, but your dock fees are based on length, and finding a 40ft dock all for yourself won’t be easy. And in the ocean i expect a 10x40 Airstream to be really bouncy and rolly.
But lets say i have a smallish residence and my 14ft “car” develops a leak (or needs cleaning or bottom paint). I most likely cannot fit it into the residence for repairs, but if my exterior lounge and bbq deck doubles as a simple drydock, getting the boat aboard (and even de-engined and flipped over) is trivial. But it’s far easier to use a floatie designed as a drydock as a bbq deck, than to make a bbq deck be a semisubmirsible drydock. As far as lightweight commercial uses, pretty much only the size matters, such as launching 16x16’s from a drydock that’s slightly larger.