Many years ago I built a "test" chair out of shop scraps when designing a chair. Red oak, white oak, maple, pine, birch, whatever I had laying in the scrap heap that was the right size piece I needed. After fine tuning the design I took the "scrap built" model and set it outside (small shop syndrome) and pretty much left it alone aside from planting my butt in it from time to time to enjoy a sunset or whatever. 5-6 years passed and aside from having to pull the chair out of the dirt to reposition it from time to time, I did absolutely nothing to it. Raw wood , left to the elements actually weathered quite well - burried in a snowbank or heating in the summer sun had little effect on it. When I bought a house and moved, I thought "that old pile should just fall apart after all these years outside" The pine was first to go- everything else was surprisingly intact- I literally had to run it over with my truck to get it to break apart. So I say build your chair out of whatever you have available in your area as an indiginous wood type (except pine or beech) Dont be afraid to go outside the box. Seems to me centuries ago they built ships out of oak ? (some of which are still in existence) Pay attention to the joinery and enjoy building your chairs.
FYI - I have seen many many chairs in the past year built using composite decking materials (heavy, but will last forever) Have fun
Elvis isn't dead, he just went home Yes, I am a joker - Take it with a grain of salt