Before I say anything about cheekpiece, what have you got installed? Barrel and lock?
There are some other things that need to be addressed before the cheekpiece is shaped.
Buttplate needs to be in place. This allows the comb and wrist line to be fleshed out.
Trigger needs to be installed. This will give you the bottom line of the stock, from grip to buttplate to be resolved.
Guard, depending on style, this will also determine the bottom line of the stock.
Step toe stock or not, the guard and trigger need to collaborate to determine the bottom profile.
Now you have the top and bottom profiles, you can now figure out where the cheekpiece goes, how big, vertical placement, yadda, yadda, yadda.
Tom