I'm not sure if there'd be too much of a difference compared with a page script; if anything, vertical should be simpler. But, were I drawing from a script other than my own, a few things which would be helpful to include would be:
Panel gap distance. (Helps a lot with pacing. 'Tight', 'Average', 'Wide' would be enough to go on.)
Scrolling background transitions, if there's anything specific the writer is envisioning there.
Panel size/location - though if you have a good artist, they're probably better placed to make decisions regarding this than the writer is.
My own script is very loose - I make panel decisions as I storyboard, not as I write. So I have nothing specific to vertical comics which I can actually show, but I do keep to a consistent style with dialogue and descriptions.
