You probably can't compare to a custom built window though you can visit some web sites for ideas. The 1x stock will be too thin for jambs or sills. Older windows used 5/4 minimum for jambs, straight grained fir- hard to find at the box stores, with a relief cut or dadoes on the backs to prevent twisting with the seasonal changes. Sills were 2x or bigger to last a long time, even so need replacing after 40 years if not protected from the elements, especially water. To use anything less will not last. The jambs should have the outside stops an integral part, to prevent entry and long life, with the inside stops removable. Do a search on "wood frame window construction" for tips.