I say build it as best as you can. Don\'t worry too much about Wards closing as in the games, but instead think out of the box. Try using masses of Plexidoors for a similar \'closing when danger\' effect. To make a Citadel in Starmade, you probably will need to make allowances for how far players can see until blocks go invisible, how big an area can be on a server before it seems hopelessly empty even at full capacity of people on there, and most importantly, how it should look despite the limitations we have. I highly recommend you try to do it though, and focus more on the features of the Citadel being there irregardless of the look.
so, what so we need?
first off, the Core/etc if A Station would likely be near the docking area to ensure ships do not attempt to crash into wherever you would otherwise place it. You will need multiple docking zones for different classes of ships. You will need to experiment how to properly mark off the docking zones to ensure clearly that certain sized ships only try to dock in certain zones.
bear in mind that certain factions would have adapted or taken over parts of the Citadel, creating districts and neighbourhoods in which that species or faction dominates, creating a unique visual style to it.
Where possible, I would recommend that the Citadel is big enough to envelope a shop, thus ensuring that there is a possible trading area in it, using the game mechanics to allow it.
you will need to think of unique visual styles that fit within e overall structure.
difficult, but not impossible.
One thing to bear in mind that it will need to be big enough that a small shuttle based (a docked core) transit system would be needed to be installed, to be true to the Citadel\'s size.
a lot of the Presidium area is high mass, decorative, with water fountains and trees, so that\'s something to consider...
anothher important consideration is that the Citadel seems to have no weapons systems of its own: it is built as a defensive structure upon which armed ships would guard against agressors. Essentially, it is the space version of a castle without any built in cannons or turrets in it: it simply has a lot of swordsmen (fighter ships) and bowmen (long range sniper missile ships) and ballista controllers (heavy missile ships) on it. This is lucky for us as it means that there is no reason to have many in-game turrets except maybe a couple here and there to reinforce weak spots in the design.
lighting will be key, I feel. One thing Bioware got right in the design was how colour affects mood. In the more seedy areas, the Citadel has more reds, more natural colours, implying decay, and the lack of artificial controls.in the high wealth districs, things are more artificially uniform and more often than not, blue with white stripes, implying law and order.
for Keepers, I recommend little structures with Bobby AI faces on them. This is your Citadel, and there\'s no need for your servants to be organic things when we have a block with a face on it that permits a lore that merges Mass Effect with Isaac Asimov\'s work if we can.
So, in time? I would say three months dedicated non-stop, planned work with a group of ten people working according to a pre-planned design brief, but working off the cuff on your own with other things going in in your life, I would say two years, due to the sheer size and detail needed to make it as awesome as it could be.