If you are referring to the main blades, the only time you'd need to work out the shape of the blade is, as tippy said, you're working with fixed pitch blades. In a collective pitch bird, the blades simply use an airfoil shape and have no AOA, you've got semi-symmetrical and symmetrical airfoils and the rotorhead determines AOA.
*EDIT: I should note that on SOME larger helicopters that aren't designed for agressive flying, the blades do have a small ammount of AOA, but this is for very big birds like the yamaha rmax and others (I think?).

If you're working with fixed pitch, the ammount of pitch you build into the rotor is entirely dependent on the motor, the voltage, and the overall headspeed you wish to achieve. Less pitch = more speed required to produce the same ammount of lift and you get a more stable (but less responsive, elevation wise) helicopter. More pitch will result in generating more lift at slower headspeeds, but it will load the motor more and the helicopter will become less stable due to a lack of gyroscopic force.

In most cases, it's a matter of finding the happy medium between the two extremes. I believe most heli manufacturers that produce fixed pitch blades have already accomplished this, so it may be worth while to just use the stock blades as a reference for initial measurements and then make any small alterations you need to from there. Less pitch is probably more desireable than more, but it will require either a larger pinion gear or faster motor to produce the right ammount of lift.

Another thing to consider is staying within the operation range of the physical mechanics of the helicopter. You could make a fixed pitch helicopter ultra stable by removing much of the pitch in the main blades to achieve very high headspeeds. But now you risk damaging the mechanics (plastic hubs, bearings, etc.) that aren't designed to operate at high rotational speeds like that.

I'm not a math whiz, as such I can't offer any numbers for you, but these are some general ideas you can consider in the future from someone who has messed extensively (to my own cost! ) with different rotor setups in fixed pitch helicopters.