Don,
If you're talking glass backed bows, the riser is from as short as 12" to as long as 16". The width is 1-1/8" to 1-3/8" wide tapering to the tips.
The grip is usually 1-7/8" deep or a bit less.
Core thickness is dependent on draw weight desired.
Bingham's is the best place to start your journey.
They have all the plans, dimensions and materials figured out for sale.
Hope this helps.