The following is taken from Version 1 of the rules, so I may tidy this up at some point:

DESIGNING YOUR OWN UNITS:

Simply come up with the appropriate stats, using the existing ones as a guideline.
As a rule of thumb:

MOVEMENT

0 Immobile units.
1 Unusually slow units such as a heavy machine-gun squad.
2 Normal speed for infantry and very slow vehicles such as tractors.
3 Normal speed for powered infantry and walkers. Also for superheavy vehicles.
4 Cruise speed for tanks and most armoured vehicles.
5+ Grav or hover vehicles. Sports cars.
9+ Superfast units like helicopters.

ARMOUR

0 Civilians and other `soft` targets.
1 Armoured infantry and civilian vehicles.
2 Light military vehicles such as Infantry Fighting Vehicles, GEV`s and `copters.
3 Fully armoured vehicles.
4+ Superheavies. Armour value 6 is about the maximum feasible unless you want to field Epic Titans.

THE FUN STATS

Remember these are based on both quantity and quality, and a single weapon may contribute to both short and long ranges.
For example, you want an IFV with a mid-calibre cannon. Cannons are typically designed to be powerful enough to penetrate the armour of a similar vehicle. This IFV has armour stat 3, so you want an attack strength of 3. You could either:
Have a LRF stat of 3.
or: Have a LRF stat of 2 and a SRF stat of 1. (lower range, same power, spread over)
You might then add a machine gun for extra point defence, adding an extra 1 to SRF.
It is important to note that the stats increase in power exponentially. Two cannons of LRF 3 would not make a total of LRF 6. Two cannons of LRF 3 would be better represented by LRF 4, with possible VLRF of 1 to represent the better hit ratio at longer ranges.
VSRF: Only assign a VSRF if the unit has specific close range weapons. Most trained infantry squads will carry anti-tank weapons and grenades at value 3. This assumes that a typical squad size is 5 to 10 men. A vehicle will have VSRF if:

• It is a riot-vehicle specifically designed for close quarter fighting (E.g. the spider mech)
• It has treads large enough to squash normal vehicles and difficult for infantry to avoid.
• It is some sort of flamethrower tank or other assaulting tank.
• It is a squad of trained infantry. The VSRF will be at least 1 for all trained infantry.

POINTS COST

Points = ARMOUR squared + SRF squared + LRF squared
If the unit has VSRF, add (VSRF * MOVEMENT)
If the unit has VLRF, add the square of that too.
Select a unit type:
ATV: Add 2*MOVEMENT
TRUNDLER: Add 2*MOVEMENT
SUPER-ATV: Add 3*MOVEMENT
TRANSPORT: Add 3*MOVEMENT
`OTHER`: Add MOVEMENT

If you multiply the final value by 10, this gives you the cost of the unit.