You have the choice to build the plane with 1/16″ sheeting on the leading edge and trailing edge, plus cap strips (D-tube wing) or a fully sheeted wing. These optional ribs have notches for 3/16 x 3/16 spars top and bottom. It’s a good idea to add 1/16″ balsa shear webs between the spars.
Or you can build per the plans with standard ribs.
Both options include a 1/8″ ply dihedral brace not shown on the plans for your optional use, plus a dihedral gauge.