A lot of people have been asking for this and rather than waiting for it in a new supplement I'd figure it could live here. 

Points are figured out thusly:

This is your 1pt baseline. A3, M6", B2, F-, D2, Mm0.  

• Every point a stat is increased, and for each keyword, add a point. 

• If you want to increase a keyword like Sniper (1) to Sniper (2) add a point. 

• For each momentum add a point.
  

• Add 1 point to gain 2 points in Fire, and 1 point per increase. So to have F3 you'd pay 2 points.

For example, say you want to create a well-armoured Death Knight. You might keep Activation at 3 (undead are probably a bit unruly). Battle is going to be 4 and Fire 2. Defense will be 4 (armoured) and Momentum 1. So far that's 7pts. We'll also give it the Unliving and Relic Guardian keywords to bring our total to 9pts. A formidable model.

Have fun creating your own models!

Very cool! I'll try make some models using this method at some point this week!

Does this need a bit of hard limit on maximums?.
If not, adding stats of 7 to a model means they can not fail a roll using that stat.
For example if a model has an activation and defense of 7 it is a practically indestructible. 

On the other hand that model, with no other "bits" on them costs 10 points, so maybe a mob of cheap fast things might be able to get the relics first, but it starts to make the abilities less meaningful and becomes a stat race.

I don't know, perhaps just a single line saying a model can't have more than 2 stats over 5 (seeing as move already starts at 6).