My DM is letting the players make up a home-world for their characters; rather than selecting a premade home-world from the books. The rules are that for every +5 we put into one stat, we take -5 from another (such as feral worlders have +5 to str and toughness, -5 to fel and wp). We also need four traits (such as hive-bound and wary for hivers); two must be positive and two negative traits.

So my idea is for a Ocean Homeworld and here is my rough-draft.

Ws 20, Bs 20, S 25, T 20, Ag 20, Int 15, Per 20, Wp 20, Fel 20.

Skills: Speak Language (Oceanic World Jargon) and Swim as a Basic Skill.

1. Agile Fighters; life in the limited confides of the floating cities or on the deck of a boat gets crowded. Those born on Oceanic worlds learn how to move gracefully in a wave of bobs and weaves. Ocean Worlders gain a +3 to agility and suffer no penalties to agility tests when running or charging though crowds.

2. What the Water Gives; For some unknown reason, oceanic worlders are compelled to have some form of water on them at all times. If a Ocean Worlder is without an source of water (i.e. a canteen or a charm that contains a small vial of water) the character suffers -10 to all actions and -10 to all wp tests to resist finding a source of water. In addition the character may start with a small vial of water on a chain (charm) or a canteen.

3. Sea Legs; Children on ocean worlds learn to swim as soon as they can walk. A Ocean Worlder removes a level of difficulty to all swimming tests as well as never suffer fatigue from swimming. In addition Ocean Worlders gain a +10 to all perception tests that are sight based and Survival tests while underwater.

4. Anhydration; Ocean World's skin constantly needs moisturizing and hydration, if a Ocean Worlder does not put oils or water on their skin it begins to dry and crack. In addition Ocean Worlder's are susceptible to heat and may never take Resistance (Heat) talent.

Hit Dice: D5+8

Fate: [1-2] 1, [3-8] 2, [ 9-10] 3.

Classes:

Assassin, Cleric, Guardsmen, Imperial Psyker, Scum,

Anhydration doesn't make much sense, especially considering that an ocean world is probably extremely hot (assuming tropical weather). Maybe they just take a penalty to tests when in a desert or other dry environment, like in the stifling hot bowels of an Adeptus Mechanicus forge. The difference being that they're used to humidity and "wet" heat, but not "dry" heat.

Also, here's some fluff blurbs for the professions, which you can alter or replace as you wish.

Assassin:

On every world in the Imperium there is a market for murder, and ocean worlds are no exception. These lone wolves often liken themselves to the fearsome macro-sharks that prowl the ocean depths, snatching their unsuspecting prey and dragging them to a watery death. These cold-blooded killers-for-hire live for the moment when their victim's lifeblood ebbs from their bodies, staining the deep blue waters with a billowing cloud of dark red.

Cleric

Priests of the Imperial Faith often prefer large, ostentatious vessels to carry them across the waves, the better to attract attention and spread the Emperor's Word. They are hardy men and women of faith, invoking the Emperor's Wrath as a mighty typhoon to smash the works of heretics and sinners to so much floating debris.

Guardsman

Pirates and other brigands roam the seas of ocean worlds, terrorizing floating cities and lonely convoys alike. The local Imperial Guard trains its troops as marines, soldiers as deadly on the pitching deck of a ship as they are lurking just beneath the waves. Their sturdy lasguns are specifically built to resist the corrosion of salt water, though troops are issued a Speargun as a backup weapon for underwater fighting.

Psyker

Ocean-born psykers often use motifs of sea animals or deadly storms to decorate their equipment and clothing, invoking the endless deep as a source of inspiration for their focus. While some find the "squid-speakers" suspicious or even downright dangerous, several psykers have used their awesome powers to gain favor among the outcasts of the ocean-dwellers, the most feared of all being Ahab Kraken-Caller of the Ninety-Nine Swords pirate fleet.

Scum

Pirates, scavengers, and other social flotsam often scrabble for survival among the literal flotsam of the waves. Many set about alone on cobbled-together vessels driven by patchwork sails or rusty, sputtering engines, while others band together to form their own crew of brigands and raiders. They are forever at odds with the marines of the PDF, and intense naval battles between them are a common sight on the dark waves.

Anhydration could be replaced with a set of gills, all depending on how much time is spent in the water. Gills would have to be covered or there would be modifiers for to fellowship as well as they might dry out and bleed. Tech priest could be used to maintain all the traditional stuff as well as any specialized equipment that would be found on your home world.