Do you need the headroom, for tall equipment or material?
An insulated ceiling would make climate control easier.
A 2nd floor would double usable floor area.
As for PV, overcast can mean 10% or 1% as much production, depending on how thick.
Either make sawdust while the sun shines, or get a large battery.
This is assuming PV is your primary power source, vs. if hydro is available.
There are fall-stop harnesses for working on roofs. Our training said you can die while dangling if there isn't help and a plan to get you back down on the ground.
I'm considering a cable strung along the ridge with pulley, so instead of being limited to an arc about a single anchor point I can have a more rectangular area available (not extending beyond the eaves.)
Of course, I'm still just considering. I bought a fall-stop but haven't hooked it up yet, and simply walk on roof when I need to (weather permitting.)