(LONG READ AND CRAP SPELLING)… you have been warned 
Intro
Not all of us in the halo community are savage beasts of the MLG (jokes) and we like to have fun on Infection, map building, being a rebel and gliching, killing our best mates in a not so friendly game of Slayer or Invasion, Its called Custom games! here are some of my ideas for halo 4 to make it ever so great! 
Contense:
.Fire fight
.Forge
.Weapons
.Duel Wielding
.Vehicles
.Custom settings
.Armor and Character skins
Fire fight
I suggest that in the options for custom fire fright, where you can select what waves will arrive (like in reach) that there are 2 teams:
UNSC
COVI
And during this you can select what teams will take part in the battle and what units will appear on each wave, As shown below (also take note in being able to chose vehicles as a unit instead of a squad);
[UNSC] -red Team
1st wave:
- marines
- Sniper Team
- warthog unit
2nd wave:
3rd wave:
Bonus wave?
[Covenant]- Blue Team
1st wave:
- Grunts
- Jackals
- Elite with Ghost
2nd wave:
3rd wave:
Bonus wave?
This way you can play fire fight in the view of an elite and if possible make it a 8-side team game like Invasion?
Also a good option to have would be how the units arrive, Explained below;
COVI
Wave 1 options
1.Grunts -> Phantom drop ship
2.Jackels -> Spirit Drop ship
3. Elite with Ghost-> Phantom drop ship with Banshee escort.
UNSC
1.Marines -> ODST drop pods
2.Sniper Team-> Falcon
3.Warthog Unit -> Pelican with Hornet escort
Obviously there would be more options smiler to these like Pelican’s on their own, randomly appearing on the map, Spirit drop ships with escorts etc… the list can go on!
I think the ability to chose two teams in fire fight would crate huge battles- you wouldn’t even have to take part… you could sit in the corner of a map and just enjoy the view of a huge scale war!
Forge
I under stand the whole argument about how forge worlds and forge maps take up a lot of memory and console enegery (or whatever) so how about an optional forge world to install to your xbox upon launch of halo 4? This map would be huge and not many restrictions due to memory being saved on your hardrive!
This map would take place on earth near New-Mombasa (or however you spell it) in the dessert- much like in levels 4 and 5 of Halo 3… Travis high way… or something like that 
In this forge world you can get every vehicle, turret, crate, barrel, weapon, wall, fence barricades you can see from any halo game belonging to the UNSC or Covi! so no more grey walls! the walls are made up from snippets of maps like power house, and the mission on halo 3 just before the flood arrives (sorry name slips my mind)
Weapons
I think the ability to place down a large verity of weapons in forge for you custom games would be amazing, it would help make many good game modes and allow different experiences in custom games and custom games only!
I the fact 343 cant be bothered or dont have enough time to make new weapons… they could copy a weapon such as the assault rifle and give it a 60 round magazine and a silencer to make a spec ops rifle with basically no effort but a small skin change, make it not appear on radar when shooting and a larger magazine size!
outer ideas are:
.Variants of the smg, Normal and ODST smg.
.Battle rifle with m16 skin.
.Magnum with D-eagle skin.
.Brute plasma rifle (a red one for those who dont play halo2) and normal.
.a batton or night stick (works like a sward) so you can make cool cops and robbers game modes!
.The shot gun but with drum mag, slightly faster firing and lowered damage.
Grenade launcher with round drum… Like on the side of falcons in Halo Reach story.
.Carbine with paintball gun skin.
.Sniper with 10 round mag and 50 Cal skin.
Could go on all day!
May I say new weapons dont need to be balanced or fair! They could be just for custom games!
I also think 343 should import all weapons from previous Halo games… so that means DMR’s and Battle Rifles in the same game! Both versions of Assault rifle… with 60 round mag and 36 round mag.
Duel Wielding
I think Duel wielding should be in Halo 4… however take the SMG for example, You can only kill someone of you are duel wielding it. To combat this and make it fair, I propose when you have one SMG(or outer duel wield-able weapon) it has fairly good accuracy, but when you duel wield it… it suffers horribly from recoil and accuracy. This way duel wielding is only useful in CQB, but you are still able to use and kill people with balance- when the weapon is not duel wielded!
Also with my ideas above- for having the Halo ODST SMG and Halo CE magnum… you can use scopes on them until you duel wield them. This way you can stop over powered weapons.
I think for custom games sake, you should be able to say if a player is able to duel wiled or not.
Vehicles
Post your ideas below and see the list grow!
The ability to change color like with the mongoose!
Just from every halo!
warthogs-guss-troop-scout-rocket-pc halo rocket hog etc…
Different shade turrets-Fuel rod- AA- halo ce shade turrets too!
Banshee-herotic banshee with no banshe bomb but faster firing plasma!
PELICAN+ Phantom
CIVI VEHICLES!-police warthog (no turret and flashing lights) - Gangster warthog(cool paint job, go faster stripe and spinning rims) - forklift- work trucks and lorries-
Ghost with duel needlers and green paint job
Destroyed Vehicles and crashed pelican/phantom.
Post your ideas below and see the list grow!
Custom Game Settings
Yea it’s not a very long list, but it needs to be said!.. 
.The ability to make a player not drop a weapon when killed… so pesky humans in infection dont steal swards >:(
.On match making there should be no bloom, but I think all weapons should have the option to suffer from bloom in custom games.
. The ability to make a player unable to duel wield weapons. (see Duel wielding)
Post ideas below and see the list grow!