Shed recommendation

too vague

I've done one side - looks pretty good. Certainly hiding a multitude of sins. How would you do corners?

You need something to nail into. I would rebate a length of square section. Easily done with a bench saw. Not so easy with a hand held circular saw on say 75mm square stuff. Someone will be along shortly with a guide design but I have managed by screwing a suitable wood strip to the normal saw guide. Alternatively bring your boards fully to the corner and hide the return with a couple of lapped vertical strips.

Word of warning. If you decorate (Sadolin etc) the exterior. Don't apply the finish before the timber is fully dried. Those boards will shrink by

Thanks - I'll go that route I think.

Ah good point. Untreated at the moment. In any case I'm making it as reversible as possible, so might come back to that in the spring.

OOI, any recommendation for a screw type - one that's rust resistant and less expensive than stainless? Doesn't need to be especially strong for this use.

snip

Pass. I have tried stainless on other exterior jobs and found they can snap off below the heads on unscrewing:-(

I've been OK with the few I've used - but I am mindful that they're not that strong. Think I may spalsh out on some - I can see this project coming apart and being put back together more than once :-)