If you get a scribe tool like this
Veritas Transfer scribe which these folks have a little spendier than i got mine for a few years back, it will make the process easier once you get the hang of scribing.
Once you get the notch cut out and the tread set in, most folks want to make the mistake of using a lag bolt to tighten it down and fill the lag hole in, which is ok, but after a time your treads will dry and shrink, as will the stringer, albeit slightly, and you end up with rocking treads which are dangerous. Laggin from the bottom can help this problem but you still have to deal with the treads closest to the floor to get a tool into to tighten lags so lagging from the top of the tread is the way to go. Using a hardwood dowel to cover the lag bolt is about the onlly way to fill it in so you can pop it out and tighten the cre after a time and then replace the cap.
I have put a couple sets in houses for folks and they do set off the house nicely.
As far as the choice of red cedar, I personally believe you should not have a problem if the logs are big enough, my grandad buikt a barn using 20 foot cedar poles for rafters in the 1920's and it is still standing today, those are about 5 inch diameter.
Your stringers should be twice the size for your treads if possible, and you need treads of about 11 inches wide if you use the standard 7-11 measure [7 inches up 11 inch tread] ive used 9's and 10's already for treads on 14 inch stringers, but did have the owner ok that project before hand. Your notches will not go half way through the log because you are on an angle, but a log when notched does lose some of its spine, different than a 2x12 board does when used as a stringer.
When done right there aint nuthin purtier either. ok in my opinion n e wayz.
William
