Not a whole lot to offer except encouragement. Never give up after the first go-round. The only thing that comes to mind with your situation is that a rooftop deck can likely dry out faster because of winds and is likely warmer because of the city in summer. Nurse those babies along. Don’t let them dry out completely at any time, keep competition from any volunteer morning glories or others to a minimum. No direct mid-day sunlight on baby seedlings…keep them partially shaded at least until they start to get established. Come to think of it…if you’ve started them inside….acclimate them as you’re moving them to the outdoors. An hour or two outside on a mild day, two to three hours the next and so on…again in a sheltered spot so they can get used to the temps, the wind, the sun etc.