Bummer on the sand, plundge pool it is. we cant have anything that would be knoticeable tbh.
as for the roof:
the set up is to have 3 steps of stone bricks up with stone steps ontop to look good, then they rise about 5 blocks in stone arches -with a stone block linning- filled with glass, from their well have another square shape as the roof hole, so i prepose we fill in with glass on the way round in a fashion that would leave a large round symetrical hole, from wich we can build an obsidian observatory/spawn point mini stronghold. We could make its ability to enter the rest of the fort be through falling water or a plundge pool at the bottom so they fall right down the centre of the main staircase. when we have the basics of the obsidian roof fort, we cover the entire roof in a carpet of magma so if an ender pearl is thrown up it will get burnt and destroyed.
Other:
The sand wall needs filling with magma in the 1 deep trench on its top
This then needs capping with stone blocks across the first inner layer and leave the outer layers as is so we can put sand on it if need be, we may have to put cactuses on the outerwall so that if someone teleports with a pearl up their they have no moving room.
The main gate needs its airlock and bridge.
The corridors from the central stairwell need digging out and smoothing, then we can decide on branching it etc.
Someone needs to fix one of our lakes, so it dosent have moving water everywere and holes underneath and to the side. Its not good practice to leave open hiding places in your base.
The towers need iron doors and a switch on the inside so we can have a one way acess to the wall etc. with doors on the bottom as well.
We need our pastures replacing in a dedicated farming level. along with the chicken coop and the farms.
The lowest levels of the fort ie that on par with the bottom of the moat should be cleared and dug entierly out and an airlock system put in place so we can repel invaders if they get in their via the bottom of the moat. I would suggest making it vaulted catacombs filled with traps.
Mines need to be established with hidden entrances tha can be sealed off to look like normal blocks so we have minning posts.
a neatherrack farm may be a good idea at some point. Or if we can grab some spawn land.
after that we can all decide on the rest as we dig out the branch corridors and all the rooms.
Also: those necro guys from the other thread/minecraft server are on our server nowadays