Easy roof access is typically the default. Landlords sometimes cut off access and a shitstorm ensues. Lawyers sometimes get involved, since it's legally hairy to cut off access to previously-accessible common areas.
> Have you ever been up to a typical apartment or condo roof top?
Several, and you can examine thousands more for yourself on Google Maps, if you like. They're not, typically, "full" of anything. They're mostly empty space.
> Sometimes there's a common area or party area - not suitable for leaving a pile of random packages though.
I'm not sure why not, but even so, there seems little risk of there being a "pile". The whole point is delivery in 30 minutes. Why would you pay for 30-minute drone delivery if you weren't going to be there to pick it up soon after?
> There's no way on earth my condo board would approve the costs involved in allowing residents up on the roof.
What costs are you imagining?
> It's hard enough for security to deal with packages at the front door.
It eludes me why you think tenants picking up their own packages from a roof is more trouble than having security (which doesn't even exist in many such buildings) deal with it.
