What's on your roof?

Rooftop real estate is going to be much more valuable on a seastead. Depending on which 'public' utilities are offered to the community, your roof will likely have one or more of the following options on it:

Sun Deck:

Some may simply want more square footage to stand on, such as a sun deck, like we saw on the first seastead in Thailand circa 2019. A nearly free option, this would require building your roof to support as much weight as your floor.

Personal Garden:

Like a Sun Deck, a year-round garden would make an excellent rooftop addition but would not be cheap to install. It would need a walkpath around it, a drainage system so it doesn't get washed away every downpour, and as much or even more floor bracing than the sundeck did to hold up the weight of all that soil and water.

Storage Shed:

Pack rats may opt to simply throw a storage shed up there, not unlike the $300 backyard barns you can buy at your local hardware store today. Again, roof bracing needs to hold it's weight.

Solar Power Generation:

Solar panels would be a major, common choice for most, because decentralized energy, even if available only half the time, is free after the cost of the panels. Batteries like Tesla's power wall would be ideal for keeping a home powered 24-7 from such panels if no central power options were offered. That does come at a pretty expense, however.

Freshwater Gathering:

The most cheap option is likely a simple rain cachement tray over your homestead, which decentralizes your fresh water source making that nearly free. Of course the H2O has to be stored somewhere, so anyone deploying a rain cachement roof will have to include a large water tank at least 1 floor beneath it. (Sucking up more real estate footage.)

Wind Power Generation:

If a seastead sees near-constant wind, a few small vertical poles could hold up windmills. One on each corner of the dwelling, in fact, perhaps more. While this isn't a cheap option it can be combined with any of the above options, because these windmills will sit higher up, on poles.

So which will it be?

Your own roof will likely be the same as every other roof around you for one good reason: The availability of lower-cost services on your seastead. If there were no cheap power or water options available, then most seasteaders would need to both cache rain and generate power upstairs, which would most likely be the rain cachement tray with a few windmills. Since rainwater is very clear, I could see a cachement tray made with solar panels at the bottom of it as well.

If your community supplies cheap power but not water, then everyone would have to do cachement but might reserve up to half the room for gardening or storage.

If your community supplies desalinated water but no central power, then few would use any cachement (again, takes up room downstairs) but everyone would likely have both solar panels and wind turbines vying for space up there.

Only if your seastead offers both, would a variety of choices prevail, giving people the option to use the space how they see fit. This would make the seastead far more interesting & able to be personalized.