The map layout:
There is a big arena, with sharp, steep, nearly verticle sides. The arena is oval shaped, and is little longer and thinner than blood gultch.
In the arena, you can design small hills and differnt obstcales and whatever. Weapons are plced in areas that are semi secluded (at least to vehicles) since you must get out of an ATV to pick up a weapon. the scenery could be as if this was a sunny/grassy feild, like in the second level of halo, or it could a dirtbike place, with dusty ground, and many ramps as bridges and things like that to do stunts. Note that in CTF, there should be absolutely GREAT vehicle chases. (You get their flag, and then spend around a minute running away from them.)
You never spawn in the arena. you allways spawn on the ridge above it. Remember how i said it has steep sides? Make sure vehicles cannot go above the steep sides. You spawn somewhere up there, with some weapons, and your ATV. Then, you ride out off the ridge into the arena. This is to prevent spawn killing.
This allows both CTF, Teams, and slayer games without roadkill spawn killing.. Teams spawn relativly near each other, but in slayer, it is not possible for enemies spawn kill each other. there are blue spawn areas and red spawn areas, if you're playing CTF. There are walls between each cubicle thingy..
I know im not explaining very well, so here is a picture:

Weapons:
First come up with the map thingy, and try it with normal weapons... then add a few other ones.
Needler, Pistol, and P-pistol may be too weak for this mod, while fuelrod and rocket launcher would be way overpowered. Maybe make a few other weapons:
Machine gun: (a holdable warthog machine gun). Underpower it abit, so it dosn't kill so fast.
Torpedo/missle launcher: It maybe has 4 missles that can shoot in quick sucession (you choose how many you shoot by how many times you click. If you click 4 times really fast, itll shoot them all near instantaneously), before it needs to reload. They home, and move around a little randomly. small explosion, medium damage. (you need 3 direct hits to kill someone). start ammo capacity is ~16 (rounds total). Actually, they home pretty well, Its just hard to hit ATVs, which are moving pretty fast. 4 barreled.
Guass rifle: A gun that shoots a small explosive round. shot speed is almost instantaneous, although fire speed is slow, and reload speed is extremely slow. its sniperish. very accurate, has a sight. You could just use beamrifle and then change projectiles
Spazz machine gun: Like the machine gun. It shoots 3 shots per round, but still shoots pretty fast. it shoots twice as slow, and its accuracy is terrible.
chain gun: It starts of shooting 2/second, but increasses to 8/second. This, and the machine guns can look relativly similar, so you don't have to design new models and animations for them.
Gatling gun: An evil looking gun that shoots spikes, like spker spikes but MUCH bigger. Fire speed, reload speed, bullet accuracy are all the same as a sniper. Not explosive, but two shots would kill. Maybe like this: (Note this is NOT my work, I think its spartan094's)
Spiker gun: you know that stuff.
shotgun: meh.... you'll need to make this weapon a little stronger, if its to be used against vehicles,
And other antivehicle weapons. Also, these weapons are just brainstorm, I'm not expecting that many new weapons... maybe 2 low explosives (torpedo launcher and guass gun) and a couple new machine guns.
You could also make proximity mines, which explode if your run over/near them. Its possible to get a one hit KO, but hard, only if you run directly above it.
Yah, so I'm looking for someone who could maybe make a map like this. Any comments?