There's a company (hypothetically) that owns a fleet of dirigibles positioned in the stratosphere, and for a fee they'll park one between you and the sun for the duration of your outdoor wedding, festival, or funeral. You book a shadow the way you'd book a tent rental.

The mechanics seem almost doable. At cruising altitude a craft big enough to cast a useful shadow on the ground would need serious surface area, and the shadow would move as the sun moves, so it's less a stationary parasol and more something doing slow continuous correction, chasing the sun's angle to keep the dark patch pinned over your lawn. Wind aloft is faster and less predictable than wind at ground level, so I think the harder problem is station-keeping, not lift.

What I can't work out is the economics of the shadow itself. You're not selling the object, you're selling an absence of light over a specific patch of grass for three hours. Does the price depend on cloud cover that day, since a passing cloud gives you the same service for free? Do you get a refund if a real cloud shows up and steals your view? And is there a minimum viable shadow size, or could someone rent a shadow just big enough to keep their drink cold?

The part that actually worries me is liability. If your rented shade drifts eight feet off target because of a gust and someone gets a sunburn they weren't expecting, who's at fault, the pilot or the wind?

Has anyone thought through the aerodynamics of a craft optimized purely for shadow-casting rather than lift efficiency? I suspect those two goals fight each other.