I bought plans from Mystic Seaport a few years ago and built a pair out of spruce. I have since broken one (towing a 19' sailboat into the wind). I haven't been rowing since because the idea of going back to the clunky store-boughts is unthinkable and my Great Auk is behind schedule.
I also bought material to make leathers from Wooden Boat. They had simple instructions for baseball type stitching which really completed the project.
My biggest error on that project was not matching the wood for both oars. One had heavier wood which made a beautiful, thin and whippy oar. The other piece was less dense and made a lighter oar which I had to leave a little thicker. I don't have a preference except that you had to use a different technique for each hand.