Pedrito: the carpenter?

[Josquius]

Are tree houses common in Europe?  For some reason I think of them as particular to the US.

Not too common, most people don't have big enough gardens to have the size trees needed.
But they certainly exist. Damn rich kids. I always wanted one. They're the height of cool for a circa 10 year old boy.
Mostly we just have tree platforms, crappy bits of wood nailed up in the trees by the kids as a crude skilless, resourceless treehouse.
Cabins on the ground are pretty common though.

[viper37]

This long seasoning delays my devious plans quite a bit.
I know a guy who does woodworking for a living, I'd better ask him if he knows of some community-owned kiln to accelerate the drying phase
 

L.

quite often, you'll see the wood planks stored for 4-5 years before they are used...
Next time you want to build a tree hours for your kids, start when your wife is still pregnant

Seriously, if it's only a tree house and you don't mind the wood twisting a little, you can skip a few months off the drying process.  Say, have the logs sawed this fall, store the wood for winter and use it next spring.