The main reason people are scared of rooftop gardening is that they think it would be so expensive. This just is not the case. Especially if rooftop gardens are included in the budget prior to constructing the building. In comparison to the price it takes to actually construct these buildings the price of the rooftop gardens will be a bargain. Most of the buildings in Seattle with rooftop space are multi million dollar facilities.
Some of these buildings actually reach into the hundreds of millions of dollars so building a garden on the roof would only be a tiny fraction of the price. At Seattle University the price of the flat screens in dormitories is greater than what it would cost to plant extensive gardens on all those roofs. There are just so many benefits of the rooftop gardens that it would be silly to think of it as an unsound investment. It would be possible to plants thousands of square feet of garden space for a mid four figure investment. Consider a hundred million dollar condo high rise.
If they were to spend ten thousand dollars creating one of the most extravagant rooftop gardens to date that was open to the people living there it would surely increase the value of their building substantially. How much is hard to say but in terms of return on investment building that garden would be a no brainer. Another benefit of spending the money to build a garden would be the media attention it would attract. In comparison to spending money on advertising the gardens would seem cheap.
There are some other reasons that hold people back from planting rooftop gardens. Sometimes the structure of the building is just inadequate to support such a weight. Other rooftops may not have access or proper draining. Although not completely necessary it is much easier to build a garden on a flat surface. Having a upside down V shaped roof is a holdup for most residential housing.