Usually the best approach is to make a sketch of the belt side view while designing the belt. At the same time start to fill out the part description. A completed part description will help identify any missing info. 

A profile may be chopped or machined as required. Please note any special modification or tolerances. Consider profile loading as well as belt loading for heavy weights and/or high acceleration. Profile shear strength is 150 PSI at the weld foot and 225 PSI normal. Belt strength may be calculated using the power transmission calculator. 

Use metric pitch belts for metric product spacing and English pitches for English spacing. Start from T10 or H pitch as it is the most common and least expensive pitch. 
Increase pitch size for strength and decrease pitch size for flexibility. 
Use AT series for increased strength without increasing pulley size too much. 
Use self-tracking where product may hit flanges or side loading is present. 
See B212 catalog pitch pages for available construction, widths and lengths. 

Belt length for a common layout with two equal size pulleys is double the center distance (CTC) plus one pulley circumference. Pulley circumference is pitch x number of teeth. Length must be evenly divisible by the pitch (whole number of teeth).