Minimum sizes are as follows:
Soprano: Tops and Backs are 3.5 inches (89mm) wide by 10.5 inches (267mm) long. Sides are 2.5 inches (64mm) wide by 15 inches (381mm) long.
Concert: Tops and Backs are 4 inches (102mm) wide by 12 (305mm) inches long. Sides are 3 inches (76mm) wide by 16.5 inches ( 419 mm) long.
Tenor: Tops and Backs are 4.75 inches (121mm) wide by 13.5 inches (343mm) long. Sides are 3.25 inches (83mm) wide by 18.5 inches (470mm) long.
Baritone: Tops and Backs are 5.25 inches (133mm) wide by 15 inches (381mm) long. Sides are 3.5 inches (89 mm) wide by 21 inches (533mm) long.
Minumum thicknesses are: Tops and Backs .120 (3 mm) inches thick. Sides are .120 inches (3mm) thick.
Tops and Backs are each made up of a two piece bookmatched set. Sides are also a two piece bookmatched set.
The above dimensions are minumums and the sets are often larger, especially in thickness. I try to get as much wood as a builder needs without wasting it in sawdust.