So I started this exercise, and decided to put it up here.  Concept is I (we) were just hired by GW, and the first task is to write a codex (yeah right, I know our first task would be much worse).

I picked Space Marines, because I know thir fluff better than anything else.  I am going to ignore the trend to dumbed down and useless choices, but go with my gut.

To begin, reread some fluff, look at the organization tables, and starting with a purely codex chapter, the first thing that leaps out at me are the army optioins:

1:  Battle Company, supported by other companies (first, reserve, or scout)

2:  First Company, dead hard force of veterans, terminators, and the best of the best

3:  Reserve companies, they rarely enter battle directly, but rarely isn't never.  Entire companies of tac, assault or dev marines.

4:  Scout Company, scouts to the left, scouts to the right.  Again, rarely fielded but an interesting army concept.

So I want to write a list that supports any of these 4 armies, without taking away from existing specialist marines, (blood angels, dark angels etc).  Something will make the formation type decision, probably part of the HQ choice.

Anyway, to get the feel of each company right, I dive into the troops, trying to make sure they hit the mark.

A battle company (and tactical reserve companies) get tactical squads as troops. 

First company gets veteran squads as troops.

Assault companies and devastator companies get the appropriate squads, same with scouts; however I think their should be some changes made to the layout of these units.  Examples: all sniping scouts would be heavy support, or assault squads with a preponderence of anti tank gear (power fists, and/or plasmas and meltas) would be heavy as well.

I would like these units to form the core of a force, and I want the battle company to remain the most flexible.  So I start tacking on requirements.  The 'core' unit of a company has a 2+ requirement on it (uh oh, I sinned, had a 2+) scouts can always be added as troops after that.  The availability of other units becomes heavily restricted, a battle company treats assault squads as fast attack, an assault company treats them as troops and fast attack, and a devastator scout or first company list treats them as unavailable.

Oh no!!  this is getting complicated, better start codifying it (since it is a codex).  Under the HQ choices, proably as a side bar, there is a note that says select a formation type from the following list: Battle, Tactical Reserve, Assault Reserve, Devastator Reserve, First Company, or Scout formation.  Might have to tack on a point cost for different formations, but I hope not.

Glancing at the existing HQs, they seem fairly solid, so they will carry over, Commander, Chaplain, Librarian.  There are some rules issues to cover later, but I don't feel the need to add in any new leaders.

Now to concentrate a bit, I will focus on the battle company, since that is the most balaced force, and the one I expect to see most often.

HQ:  Commander, Chaplain, Librarian

Elite:  Termminator Squad (First Company Support), Terminator Assault Squad (First Comany Support), Company Dreadnought, Company Veterans

Troops: 2+ Tactical Squads, Scout Squads (10th company support)

Fast Attack: Assault Squads, Bike Squads, Land Speeder Squadrons, Scout Bikes, Attack Bikes

Heavy Support: 0-1 Land Raider (or LR Crusader),  Predator (either), Dev Squad, Whirlwind, Vindicator

I need to find a place to stick tech marines and apothecaries, neither of which I feel should be locked into command squads.

Never heard of any other space marine units worth mentioning (effectivly removing the Hunter AA tank and Thunderhawk variants for now)

Now I think about special rules:  These guys are suppose to be hard, but not the best of the best (that is the first company) so Know No Fear should be sufficient.  I think combat squads is an intereting and characterful touch, but I also think that assuming that the army starts every battle at full strength is dumb.  So squads that are a full 10 men may be split into 2 5 man combat squads.

While I am thinking about it, Transports:  Rhinos 12 men, Razorbacks 6, Drop Pods 10, Land Raiders 12 (15 for crusaders) and if I find a place for them in the Rules, Boarding Torpedoes 5 terminators (which for those who are really old as dirt know this to be the origin of the 5 man terminator squad.)

But anyway, I have a core force.  Now for variation:

First Company: Lose access to tac squads, all fast attack, and dev squads.  Company Veterans become troops 2+, and certain additional options become available.  Maybe if they take a dedicated transport they can count as troops or fast attack, and extra heavy weapons makes them heavy support.

Scouts: lose access to just about everything.  Tac squads become elite (must take infiltrate for X per man), normal scouts ar troops, scout bikes are fast, and "heavy scouts" are heavy support.  I would say that any scout squad with more than 1/2 its number in heavy weapons becomes heavy.

Similar effects for the reserve companies.  Assault companies get lots of assault but face some real challenges elsewhere (fire power mainly, having to run up to every tank is a liability)

--That is all for now, nxt time I post I will start covering specific units --

Finally, make sure that you leave room for the gratuatous asskissing, and patting yourself on the back for putting pen to paper.

Seriously though, You can't do as bad a job as some of the codex have become, Hope something comes of your work.

good luck to you.

Anyway, as promised, a look at my perception of a unit, in this case the ubiquitous Tactical Squad:

340 / 1000 marines are tactical marines.  They form the foundation of any decent army.  And you should almost never leave homeworld without them (specialized companies being the exception.

Unit size:  The Codex Astartes says each squad should be 10 men.  It has also been implied that each squad has a minimum combat strength of 5, otherwise it is too weak to participate.  The squad should always be lead into battle by a squad leader (sargeant), even if it is only a brevet rank.  And I don't think Marines get promoted based on picking the long straw, so rules for "standard" vs "veteran" sargeants are right out.

1 Veteran sarge, and 4 marines - XX points (i'll get around to points eventually) up to 5 additional marines XY points each

Taking a full squad of 10 should be rewarded, but assuming that every marine survived the last battle is dumb - so squads of 10 men may be split into 2 five man combat squads, with all that entails...

Basic Equipment: These are THE MARINES, not some mamby pamby pack of imperial guardsment.  They spend 20 hours a day training in all the forms of war.  Bolter, Bolt Pistol, Close Combat Weapon, Frag Grenades, Krak Grenades, Food, Water, Beer Cozy, Cooking Area Water Provision Device...

Really, Bolter, bolt pistol, CCW, frag and krak, standard

Upgrades:  A single marine (not the sarge) may choose an item from this list to replace their bolter or their bolt pistol and CCW: flamer, plasma gun, melta gun (points)

[[Aside: I think all flamers would be a lot more attractive if they used the inferno cannon rules.  Standard flamer 12 inch range, heavy flamer 18 inch range...  place the template...  but that is just me]]

A single marine (not the sarge) may choose an item from this list to replace theit bolter or their bolt pistol and CCW: Heavy Bolter, Missile Launcher, LasCannon, Plasma Cannon, Multi Melta, flamer, plasma gun or melta gun (points)  Note here, the points for heavy weapons should be less than that from devastators since a tac squad will be moving around and firing less often, and the price of special weapons (flamer, etc...) should be higher if they want to take a second.  A single plasma gun may be 6 points, the second should be 10.

Sarge: The sarge already has +1 leadership and +1 attack included, so no need for termie honors.

Sarge Weapons-

may replace the bolter with: combi-melta, combi-plas, combi-flam, storm bolter,  

may replace bolt pistol with plasma pistol

may replace CCW with power weapon, power fist, thunder hammer, single lightning claw

may replace all weapons with: paired lightning claws

wargear:

melta bombs

purity seals (automatically pass a leadership test as though rolling a 2 once per game)

bionics

upgrade any one weapon to master crafted

auspex: (grants heightened senses USR)

Storm shield - 4+ invulnerable save in close combat

maybe more...

Transport:

Rhino, Razorback (up to 6), Drop Pod