As I interpret the plans, the wing ribs appear to be cut from 1/8" Balsa sheet. You might consider using 1/8" aircraft ply for the inner 2 or 3 ribs on each wing. The control surfaces, (elevator, rudder, horizontal and vertical stabs) appear to be built up from 1/4"x1/2" balsa sticks, with an inner layer of 1/16" balsa sheeting. After its built up, it is sanded to the final airfoil shape shown on the plans.

I obtained these dimensions by opening the files in a drawing program and using the dimension feature in the program to make the measurements.

Brad