That is actually a hard question as there would be so many I would have to think about it and make a list. Off the top of my head...
I've always wanted to build a log cabin or something similar. Even if it ended up being an animal shelter I think it would be neat.
Also blacksmithing would be cool.
Blacksmithing would absolutely be a great skill. A friend of mine makes tools and man are they gorgeous. Its a skill I dont feel called to but definitely value.
Log building...goodness yes. Agreed, even if its a basic shelter. That's one I'd like to try out next year. Hopefully first for a tool shed. Then something bigger down the road.
A tool shed would be a great use for a log building. It would look really cool too! Reminds me of the old homesteads.