Hall,
Take what Jackie said (he's right most of the time), the only two basic dimensions are just the forearm width (3" max) and the angle of the buttstock. Search for stock pic in IBS/NBRSA/WBSF website. The other dimensions & how the stock looks like is "up to you".
What the material(s) would be?
All materials can be shaped to your liking, just be aware with its/their characteristics.
I assume that this is your first project since you (still) ask dimensions.
I prefer a low rider stock myself (less torque upon recoil).
Make sure the stock is strong & rigid enough.
Straight is a must (to track well). Action, barrel channel, trigger/guard cutout, & outside lines (especially the bottom of the forearms and the toe/butt) will be much better done by a milling machine as it's more precise. If you don't have a milling, make a "center line" along the longitudinal sides, for your reference. Especially if you make it from a solid blank wood, but I doubt it due to the weight limitation.
The forearm should be flat. You don't want a convex for a BR stock. Concave is illegal.
Stock weight in the range of 22-27 oz for LV gun. Lighter is not always better, just make sure it fits the 10.5 lbs total weight limit. You need to know how many lbs/oz is your barreled action + trigger/hanger + scope + rings. Prepare about 2 oz less, to be safe. More if you use a tuner. In a LV gun, every ounce is count.
You can add weight system (from LV to HV), if you like it.
The lower the center of gravitiy of the stocked rifle the better.
Alinwa is right, draw the stock on a paper. Make some sketches and then choose one.
Good luck,
seb.